diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,13 @@
 The serialization format carries its own version tag, independent of the package
 version; any change to it is recorded here explicitly.
 
+## 1.2.0.1
+
+* Admit GHC 9.8 as a tested compiler by spelling the package language as
+  `GHC2021` plus `DerivingStrategies`, accepting `base-4.19`, and qualifying
+  strict list folds through `Data.List`. This restores Hackage build and
+  documentation generation without changing the API or binary format.
+
 ## 1.2.0.0
 
 * Add exact rational planar regions and labelled common refinement with one
diff --git a/bench/dcel/Moonlight/Triangulation/DcelBench.hs b/bench/dcel/Moonlight/Triangulation/DcelBench.hs
--- a/bench/dcel/Moonlight/Triangulation/DcelBench.hs
+++ b/bench/dcel/Moonlight/Triangulation/DcelBench.hs
@@ -15,6 +15,7 @@
   )
 import Control.DeepSeq (force)
 import Control.Exception (evaluate)
+import qualified Data.List as List
 import qualified Data.Vector as V
 import Moonlight.Triangulation
 import Moonlight.Triangulation.FloodFillIterator (edgesInCircle)
@@ -122,7 +123,7 @@
       "alpha-face-membership"
       ( evaluate
           ( force
-              ( foldl'
+              ( List.foldl'
                   (\count face ->
                      if containsFace face
                        then count + 1
diff --git a/bench/support/BenchSupport.hs b/bench/support/BenchSupport.hs
--- a/bench/support/BenchSupport.hs
+++ b/bench/support/BenchSupport.hs
@@ -14,6 +14,7 @@
 
 import Control.DeepSeq (NFData, force)
 import Control.Exception (evaluate)
+import qualified Data.List as List
 import Data.Word (Word64)
 import qualified Data.Vector as V
 import GHC.Clock (getMonotonicTimeNSec)
@@ -95,7 +96,7 @@
   -> Int
 latticeFaceBand triangulation face =
   let xSum =
-        foldl'
+        List.foldl'
           (\accumulator vertex -> accumulator + pointX (vertexPoint triangulation vertex))
           0
           (faceVertices triangulation face)
diff --git a/moonlight-triangulation.cabal b/moonlight-triangulation.cabal
--- a/moonlight-triangulation.cabal
+++ b/moonlight-triangulation.cabal
@@ -1,6 +1,6 @@
 cabal-version:       3.4
 name:                moonlight-triangulation
-version:             1.2.0.0
+version:             1.2.0.1
 synopsis:            Delaunay meshes and exact planar-region algebra.
 description:         Delaunay and constrained Delaunay triangulation as a lawful
                      finite-set algebra, together with exact rational planar
@@ -29,7 +29,8 @@
 homepage:            https://github.com/PaleRoses/moonlight
 bug-reports:         https://github.com/PaleRoses/moonlight/issues
 build-type:          Simple
-tested-with:         GHC == 9.10.3
+tested-with:         GHC == 9.8.4
+                     GHC == 9.10.3
                      GHC == 9.12.4
                      GHC == 9.14.1
 extra-doc-files:
@@ -63,7 +64,9 @@
   manual: True
 
 common shared-properties
-  default-language: GHC2024
+  default-language: GHC2021
+  default-extensions:
+    DerivingStrategies
   ghc-options:
     -Wall
     -Wcompat
@@ -97,7 +100,7 @@
     Moonlight.Triangulation.Internal.PackedIndex
     Moonlight.Triangulation.Internal.FaceQueue
   build-depends:
-    base >= 4.20 && < 5
+    base >= 4.19 && < 5
     , containers >= 0.8 && < 0.9
     , deepseq >= 1.5 && < 1.6
     , vector >= 0.13 && < 0.14
@@ -157,7 +160,7 @@
   other-modules:
     Moonlight.Triangulation.Internal.Region.Bounds
   build-depends:
-    base >= 4.20 && < 5
+    base >= 4.19 && < 5
     , containers >= 0.8 && < 0.9
     , deepseq >= 1.5 && < 1.6
     , primitive >= 0.9 && < 0.10
@@ -215,7 +218,7 @@
     Moonlight.Triangulation.Internal.Minkowski.Convex
     Moonlight.Triangulation.Internal.Minkowski.Types
   build-depends:
-    base >= 4.20 && < 5
+    base >= 4.19 && < 5
     , containers >= 0.8 && < 0.9
     , deepseq >= 1.5 && < 1.6
     , primitive >= 0.9 && < 0.10
@@ -234,7 +237,7 @@
   exposed-modules:
     Moonlight.Triangulation.Parallel
   build-depends:
-    base >= 4.20 && < 5
+    base >= 4.19 && < 5
     , async >= 2.2 && < 2.3
     , deepseq >= 1.5 && < 1.6
     , moonlight-triangulation:core
@@ -252,7 +255,7 @@
   exposed-modules:
     Moonlight.Triangulation.Serialization
   build-depends:
-    base >= 4.20 && < 5
+    base >= 4.19 && < 5
     , binary >= 0.8 && < 0.9
     , bytestring >= 0.12 && < 0.13
     , containers >= 0.8 && < 0.9
@@ -278,7 +281,7 @@
   other-modules:
     Moonlight.Triangulation.Internal.InterpolationWorkspace
   build-depends:
-    base >= 4.20 && < 5
+    base >= 4.19 && < 5
     , deepseq >= 1.5 && < 1.6
     , primitive >= 0.9 && < 0.10
     , vector >= 0.13 && < 0.14
@@ -293,7 +296,7 @@
   exposed-modules:
     Moonlight.Triangulation
   build-depends:
-    base >= 4.20 && < 5
+    base >= 4.19 && < 5
     , moonlight-triangulation:core
     , moonlight-triangulation:dcel
     , moonlight-triangulation:build
@@ -307,7 +310,7 @@
   exposed-modules:
     Moonlight.Triangulation.Foreign.ABI
   build-depends:
-    base >= 4.20 && < 5
+    base >= 4.19 && < 5
     , vector >= 0.13 && < 0.14
     , moonlight-triangulation
     , moonlight-triangulation:build
@@ -326,7 +329,7 @@
   install-includes:
     moonlight_triangulation.h
   build-depends:
-    base >= 4.20 && < 5
+    base >= 4.19 && < 5
     , moonlight-triangulation:ffi >= 1.2 && < 1.3
   ghc-options: -threaded
   if os(windows)
@@ -348,7 +351,7 @@
 common triangulation-test-properties
   import: shared-properties
   build-depends:
-    base >= 4.20 && < 5
+    base >= 4.19 && < 5
     , deepseq >= 1.5 && < 1.6
     , vector >= 0.13 && < 0.14
     , primitive >= 0.9 && < 0.10
@@ -508,7 +511,7 @@
   main-is: Main.hs
   hs-source-dirs: test/ffi
   build-depends:
-    base >= 4.20 && < 5
+    base >= 4.19 && < 5
     , moonlight-triangulation:ffi
 
 -- This component owns only cross-slice compile coherence.  Behavioral ownership
@@ -553,7 +556,7 @@
   -- and no benchmark slice may name it again.
   ghc-options: -threaded -rtsopts "-with-rtsopts=-T"
   build-depends:
-    base >= 4.20 && < 5
+    base >= 4.19 && < 5
     , deepseq >= 1.5 && < 1.6
     , vector >= 0.13 && < 0.14
     , moonlight-triangulation
diff --git a/src-build/Moonlight/Triangulation/Internal/Cdt/Split.hs b/src-build/Moonlight/Triangulation/Internal/Cdt/Split.hs
--- a/src-build/Moonlight/Triangulation/Internal/Cdt/Split.hs
+++ b/src-build/Moonlight/Triangulation/Internal/Cdt/Split.hs
@@ -24,6 +24,7 @@
 
 import Control.Monad.ST (ST, runST)
 import Data.Bits (xor)
+import qualified Data.List as List
 import qualified Data.Vector as V
 import qualified Moonlight.Triangulation.Dcel as Dcel
 import Moonlight.Triangulation.Handles.HandleDefs
@@ -171,7 +172,7 @@
 splitCensus triangulation (from, to)
   | from == to = (0, Nothing)
   | otherwise =
-      foldl'
+      List.foldl'
         countCrossing
         (0, Nothing)
         (getConflictingEdgesBetweenVertices triangulation from to)
diff --git a/src-build/Moonlight/Triangulation/Internal/Minkowski/Convex.hs b/src-build/Moonlight/Triangulation/Internal/Minkowski/Convex.hs
--- a/src-build/Moonlight/Triangulation/Internal/Minkowski/Convex.hs
+++ b/src-build/Moonlight/Triangulation/Internal/Minkowski/Convex.hs
@@ -19,6 +19,7 @@
 
 import Control.Monad (foldM)
 import Data.Bifunctor (first)
+import qualified Data.List as List
 import Data.List.NonEmpty (NonEmpty (..))
 import qualified Data.List.NonEmpty as NonEmpty
 import qualified Data.Set as Set
@@ -157,7 +158,7 @@
   let points = convexPolygonPoints polygon
       count = fromIntegral (NonEmpty.length points)
       (sumX, sumY) =
-        foldl'
+        List.foldl'
           (\(accumulatedX, accumulatedY) point ->
              let (x, y) = exactPointCoordinates point
               in (accumulatedX + x, accumulatedY + y))
@@ -222,8 +223,8 @@
   case Set.toAscList (Set.fromList submitted) of
     firstPoint : secondPoint : thirdPoint : remaining ->
       let ordered = firstPoint : secondPoint : thirdPoint : remaining
-          lower = dropFinal (reverse (foldl' hullStep [] ordered))
-          upper = dropFinal (reverse (foldl' hullStep [] (reverse ordered)))
+          lower = dropFinal (reverse (List.foldl' hullStep [] ordered))
+          upper = dropFinal (reverse (List.foldl' hullStep [] (reverse ordered)))
        in case lower <> upper of
             firstHullPoint : secondHullPoint : thirdHullPoint : hullTail ->
               Just (firstHullPoint :| (secondHullPoint : thirdHullPoint : hullTail))
@@ -252,7 +253,7 @@
       supportPoint =
         case kernelPoints of
           initial :| remaining ->
-            foldl'
+            List.foldl'
               (\selected candidate ->
                  if directionPointCross direction candidate
                       < directionPointCross direction selected
diff --git a/src-build/Moonlight/Triangulation/Internal/Overlay/Arrangement.hs b/src-build/Moonlight/Triangulation/Internal/Overlay/Arrangement.hs
--- a/src-build/Moonlight/Triangulation/Internal/Overlay/Arrangement.hs
+++ b/src-build/Moonlight/Triangulation/Internal/Overlay/Arrangement.hs
@@ -21,6 +21,7 @@
 
 import Data.Bifunctor (first)
 import Data.List (sortBy)
+import qualified Data.List as List
 import Data.List.NonEmpty (NonEmpty (..))
 import qualified Data.List.NonEmpty as NonEmpty
 import qualified Data.Map.Strict as Map
@@ -324,7 +325,7 @@
   grouped =
     V.ifoldl'
       (\groups sourceIndex source ->
-         foldl'
+         List.foldl'
            (insertAtomic source)
            groups
            (consecutivePairs (exactSegmentSplitPoints plan (ExactSweepSegmentId sourceIndex))))
@@ -357,7 +358,7 @@
         , leftSources
         , rightSources
         ) =
-          foldl'
+          List.foldl'
             collectContribution
             (Set.empty, Set.empty, Set.empty, Set.empty, Set.empty, Set.empty)
             contributions
diff --git a/src-build/Moonlight/Triangulation/Internal/Overlay/Resident.hs b/src-build/Moonlight/Triangulation/Internal/Overlay/Resident.hs
--- a/src-build/Moonlight/Triangulation/Internal/Overlay/Resident.hs
+++ b/src-build/Moonlight/Triangulation/Internal/Overlay/Resident.hs
@@ -16,6 +16,7 @@
 import Data.Bifunctor (first)
 import Data.Foldable (traverse_)
 import Data.List (partition, sort, sortBy)
+import qualified Data.List as List
 import Data.List.NonEmpty (NonEmpty (..))
 import qualified Data.List.NonEmpty as NonEmpty
 import qualified Data.Map.Strict as Map
@@ -802,7 +803,7 @@
   -> Maybe (OverlayCellSupport leftLabel rightLabel)
 supportFromPairs pairs = do
   let (leftLabels, rightLabels) =
-        foldl'
+        List.foldl'
           (\(left, right) (leftLabel, rightLabel) ->
              (Set.insert leftLabel left, Set.insert rightLabel right))
           (Set.empty, Set.empty)
diff --git a/src-build/Moonlight/Triangulation/Minkowski.hs b/src-build/Moonlight/Triangulation/Minkowski.hs
--- a/src-build/Moonlight/Triangulation/Minkowski.hs
+++ b/src-build/Moonlight/Triangulation/Minkowski.hs
@@ -27,6 +27,7 @@
 import Control.Monad (filterM)
 import Data.Bifunctor (first)
 import qualified Data.IntMap.Strict as IntMap
+import qualified Data.List as List
 import qualified Data.Map.Strict as Map
 import Data.List.NonEmpty (NonEmpty (..))
 import qualified Data.List.NonEmpty as NonEmpty
@@ -559,19 +560,19 @@
 coordinateBitGrowth inputs output =
   max 0
     ( regionCoordinateBits output
-        - foldl' (\maximumBits -> max maximumBits . regionCoordinateBits) 0 inputs
+        - List.foldl' (\maximumBits -> max maximumBits . regionCoordinateBits) 0 inputs
     )
 
 regionCoordinateBits :: PlanarRegion -> Int
-regionCoordinateBits = foldl' componentBits 0 . planarRegionComponents
+regionCoordinateBits = List.foldl' componentBits 0 . planarRegionComponents
  where
   componentBits maximumBits component =
-    foldl'
+    List.foldl'
       loopBits
       maximumBits
       (polygonOuterLoop component : polygonHoleLoops component)
   loopBits maximumBits =
-    foldl' pointBits maximumBits . exactLoopPoints
+    List.foldl' pointBits maximumBits . exactLoopPoints
   pointBits maximumBits point =
     let (x, y) = exactPointCoordinates point
      in max maximumBits (max (rationalBits x) (rationalBits y))
diff --git a/src-core/Moonlight/Triangulation/Internal/Dyadic.hs b/src-core/Moonlight/Triangulation/Internal/Dyadic.hs
--- a/src-core/Moonlight/Triangulation/Internal/Dyadic.hs
+++ b/src-core/Moonlight/Triangulation/Internal/Dyadic.hs
@@ -21,6 +21,7 @@
   , shiftL
   , shiftR
   )
+import qualified Data.List as List
 import Data.Word (Word64)
 #if WORD_SIZE_IN_BITS == 64
 import GHC.Exts
@@ -59,7 +60,7 @@
 type Decoded = (Integer, Int)
 
 commonExponent :: [Decoded] -> Int
-commonExponent = foldl' step 0
+commonExponent = List.foldl' step 0
  where
   step :: Int -> Decoded -> Int
   step !current (!mantissa, !power)
diff --git a/src-core/Moonlight/Triangulation/Internal/PageDirectory.hs b/src-core/Moonlight/Triangulation/Internal/PageDirectory.hs
--- a/src-core/Moonlight/Triangulation/Internal/PageDirectory.hs
+++ b/src-core/Moonlight/Triangulation/Internal/PageDirectory.hs
@@ -19,6 +19,7 @@
 
 import Control.DeepSeq (NFData)
 import Data.Bits (shiftL, shiftR, (.&.))
+import qualified Data.List as List
 import qualified Data.Vector as V
 import qualified Data.Vector.Mutable as MV
 import GHC.Generics (Generic)
@@ -130,7 +131,7 @@
     , directorySize = length entries
     }
  where
-  !largest = foldl' (\largestKey (key, _) -> max largestKey key) firstKey remainingEntries
+  !largest = List.foldl' (\largestKey (key, _) -> max largestKey key) firstKey remainingEntries
   !height = heightFor 0
   heightFor !candidate
     | largest < capacity candidate = candidate
@@ -147,7 +148,7 @@
               step (children, unconsumed) index =
                 let (!child, !beyond) = build (level - 1) (base + index * childSpan) unconsumed
                  in (child : children, beyond)
-              (!reversed, !left) = foldl' step ([], remaining) [0 .. fanout - 1]
+              (!reversed, !left) = List.foldl' step ([], remaining) [0 .. fanout - 1]
            in (Fanout (V.fromListN fanout (reverse reversed)), left)
 
 directoryToAscList :: PageDirectory a -> [(Int, a)]
diff --git a/src-dcel/Moonlight/Triangulation/FloodFillIterator.hs b/src-dcel/Moonlight/Triangulation/FloodFillIterator.hs
--- a/src-dcel/Moonlight/Triangulation/FloodFillIterator.hs
+++ b/src-dcel/Moonlight/Triangulation/FloodFillIterator.hs
@@ -44,6 +44,7 @@
 import qualified Data.IntMap.Strict as IntMap
 import qualified Data.IntSet as IntSet
 import Data.List (partition, unfoldr)
+import qualified Data.List as List
 import Data.List.NonEmpty (NonEmpty (..))
 import qualified Data.Sequence as Seq
 import qualified Data.Vector as V
@@ -221,7 +222,7 @@
   ]
  where
   edges = edgesInShape triangulation metric
-  set = foldl' addEndpoints IntSet.empty edges
+  set = List.foldl' addEndpoints IntSet.empty edges
   addEndpoints acc edge =
     let (VertexId from, VertexId to) = undirectedEndpoints triangulation edge
      in IntSet.insert (fromIntegral from) (IntSet.insert (fromIntegral to) acc)
@@ -246,7 +247,7 @@
    in (reverse faces, accepted)
  where
   valid face@(FaceId value) = face /= outerFace && fromIntegral value < numFaces triangulation
-  (initialStack, initialVisited) = foldl' enqueueStart ([], IntSet.empty) starts
+  (initialStack, initialVisited) = List.foldl' enqueueStart ([], IntSet.empty) starts
 
   enqueueStart state face
     | valid face = enqueue face state
@@ -544,7 +545,7 @@
     OnEdge edge -> filter (/= outerFace) [incidentFace triangulation edge, incidentFace triangulation (reverseEdge edge)]
     OnVertex vertex ->
       intSetToFaces
-        (foldl' (\set edge -> let FaceId value = incidentFace triangulation edge in if value == 0 then set else IntSet.insert (fromIntegral value) set) IntSet.empty (vertexOutgoingEdges triangulation vertex))
+        (List.foldl' (\set edge -> let FaceId value = incidentFace triangulation edge in if value == 0 then set else IntSet.insert (fromIntegral value) set) IntSet.empty (vertexOutgoingEdges triangulation vertex))
     OutsideConvexHull _ ->
       [ incidentFace triangulation (reverseEdge edge)
       | edge <- faceDirectedEdges triangulation outerFace
diff --git a/src-dcel/Moonlight/Triangulation/Internal/BoundaryCycle.hs b/src-dcel/Moonlight/Triangulation/Internal/BoundaryCycle.hs
--- a/src-dcel/Moonlight/Triangulation/Internal/BoundaryCycle.hs
+++ b/src-dcel/Moonlight/Triangulation/Internal/BoundaryCycle.hs
@@ -15,6 +15,7 @@
 
 import Data.List.NonEmpty (NonEmpty (..))
 import Data.List (tails)
+import qualified Data.List as List
 import qualified Data.List.NonEmpty as NonEmpty
 
 -- | Remove precisely the vertices admitted by @isRedundant@ until a fixed
@@ -50,7 +51,7 @@
       [] -> Left (obstruction values)
       firstTriple : remainingTriples ->
         let (previousValue, current, nextValue) =
-              foldl' chooseLeast firstTriple remainingTriples
+              List.foldl' chooseLeast firstTriple remainingTriples
             winding = orientation previousValue current nextValue
          in case (winding, values) of
               (EQ, _) -> Left (obstruction values)
@@ -82,7 +83,7 @@
  where
   asList = NonEmpty.toList values
   minimumKey =
-    foldl'
+    List.foldl'
       (\selected candidate -> min selected (key candidate))
       (key (NonEmpty.head values))
       (NonEmpty.tail values)
@@ -128,7 +129,7 @@
 cyclicTriples values =
   case values of
     initial : second : remaining ->
-      let final = foldl' (\_ current -> current) initial (second : remaining)
+      let final = List.foldl' (\_ current -> current) initial (second : remaining)
        in zip3
             (final : values)
             values
diff --git a/src-dcel/Moonlight/Triangulation/Internal/ExactSegmentEvents.hs b/src-dcel/Moonlight/Triangulation/Internal/ExactSegmentEvents.hs
--- a/src-dcel/Moonlight/Triangulation/Internal/ExactSegmentEvents.hs
+++ b/src-dcel/Moonlight/Triangulation/Internal/ExactSegmentEvents.hs
@@ -23,6 +23,7 @@
 import Control.Applicative ((<|>))
 import Control.Monad (filterM, foldM)
 import Data.List (sortBy)
+import qualified Data.List as List
 import qualified Data.IntMap.Strict as IntMap
 import qualified Data.Map.Strict as Map
 import Data.Map.Strict (Map)
@@ -210,7 +211,7 @@
       b = negate deltaX
       c = deltaX * fromY - deltaY * fromX
       denominators = map exactRationalDenominator [a, b, c]
-      commonDenominator = foldl' lcm 1 denominators
+      commonDenominator = List.foldl' lcm 1 denominators
       integerCoefficient coefficient =
         exactRationalNumerator coefficient
           * (commonDenominator `quot` exactRationalDenominator coefficient)
@@ -513,7 +514,7 @@
       case ordered of
         [] -> Right state
         lowest : remaining ->
-          let highest = foldl' (\_ current -> current) lowest remaining
+          let highest = List.foldl' (\_ current -> current) lowest remaining
               below = statusPredecessor currentX lowest status
               above = statusSuccessor currentX highest status
            in scheduleMaybePair metas currentX below (Just (metaId lowest)) state
diff --git a/src-dcel/Moonlight/Triangulation/Internal/Region/Bounds.hs b/src-dcel/Moonlight/Triangulation/Internal/Region/Bounds.hs
--- a/src-dcel/Moonlight/Triangulation/Internal/Region/Bounds.hs
+++ b/src-dcel/Moonlight/Triangulation/Internal/Region/Bounds.hs
@@ -14,6 +14,7 @@
   ) where
 
 import Data.List (sortOn, tails)
+import qualified Data.List as List
 import Data.List.NonEmpty (NonEmpty (..))
 import qualified Data.IntMap.Strict as IntMap
 import Moonlight.Triangulation.Exact
@@ -35,7 +36,7 @@
 
 exactLoopBounds :: ExactLoop -> ExactBounds
 exactLoopBounds (ExactLoop (firstPoint :| remaining)) =
-  foldl' extend (pointBounds firstPoint) remaining
+  List.foldl' extend (pointBounds firstPoint) remaining
  where
   extend bounds point = boundsUnion bounds (pointBounds point)
 
@@ -48,7 +49,7 @@
     [] -> Nothing
     firstComponent : remaining ->
       Just
-        ( foldl'
+        ( List.foldl'
             (\bounds component -> boundsUnion bounds (componentBounds component))
             (componentBounds firstComponent)
             remaining
diff --git a/src-dcel/Moonlight/Triangulation/Region.hs b/src-dcel/Moonlight/Triangulation/Region.hs
--- a/src-dcel/Moonlight/Triangulation/Region.hs
+++ b/src-dcel/Moonlight/Triangulation/Region.hs
@@ -28,6 +28,7 @@
 import Data.Bifunctor (first)
 import Data.Foldable (traverse_)
 import Data.List (sort)
+import qualified Data.List as List
 import qualified Data.Map.Strict as Map
 import Data.Map.Strict (Map)
 import Data.List.NonEmpty (NonEmpty (..))
@@ -263,7 +264,7 @@
 loopWinding :: ExactLoop -> Ordering
 loopWinding (ExactLoop points) =
   exactSignum
-    ( foldl'
+    ( List.foldl'
         (\signedArea (from, to) ->
            signedArea + exactPointCross from to)
         0
diff --git a/src-dcel/Moonlight/Triangulation/Valuation.hs b/src-dcel/Moonlight/Triangulation/Valuation.hs
--- a/src-dcel/Moonlight/Triangulation/Valuation.hs
+++ b/src-dcel/Moonlight/Triangulation/Valuation.hs
@@ -35,6 +35,7 @@
 import Data.Bifunctor (first)
 import Data.Bits (shiftL)
 import Data.Foldable (foldlM)
+import qualified Data.List as List
 import Data.List.NonEmpty (NonEmpty (..))
 import qualified Data.IntMap.Strict as IntMap
 import qualified Data.IntSet as IntSet
@@ -185,7 +186,7 @@
       (IntSet.toAscList selectedEdges)
   assembleValuations
     (IntMap.size points - IntSet.size selectedEdges + IntSet.size selectedFaces)
-    (foldl' (+) 0 faceDoubleAreas)
+    (List.foldl' (+) 0 faceDoubleAreas)
     (normalizeLengthContributions id edgeContributions)
 
 regionValuations :: PlanarRegion -> Either ValuationError PlanarValuations
@@ -200,7 +201,7 @@
       hasPotentialBoundaryContacts
       componentBoundaries
   let doubleArea =
-        foldl'
+        List.foldl'
           (\area component -> area + componentDoubleArea component)
           0
           components
@@ -292,14 +293,14 @@
 
 componentDoubleArea :: PolygonComponent -> ExactRational
 componentDoubleArea component =
-  foldl'
+  List.foldl'
     (\area loop -> area + loopDoubleArea loop)
     0
     (polygonOuterLoop component : polygonHoleLoops component)
 
 loopDoubleArea :: ExactLoop -> ExactRational
 loopDoubleArea (ExactLoop points) =
-  foldl'
+  List.foldl'
     (\area (from, to) -> area + exactPointCross from to)
     0
     (cyclePairs points)
@@ -325,7 +326,7 @@
     ]
  where
   coefficientsBySquare =
-    foldl' accumulateContribution Map.empty contributions
+    List.foldl' accumulateContribution Map.empty contributions
   accumulateContribution coefficients value =
     case contribution value of
       (coefficient, square)
diff --git a/src-embedding/Moonlight/Triangulation/Internal/Overlay/Embedding.hs b/src-embedding/Moonlight/Triangulation/Internal/Overlay/Embedding.hs
--- a/src-embedding/Moonlight/Triangulation/Internal/Overlay/Embedding.hs
+++ b/src-embedding/Moonlight/Triangulation/Internal/Overlay/Embedding.hs
@@ -23,6 +23,7 @@
 
 import Control.DeepSeq (NFData)
 import Data.List (sort, tails)
+import qualified Data.List as List
 import Data.List.NonEmpty (NonEmpty (..))
 import qualified Data.List.NonEmpty as NonEmpty
 import Data.Map.Strict (Map)
@@ -389,7 +390,7 @@
   case memberships of
     firstMembership : secondMembership : remainingMemberships ->
       let finalMembership =
-            foldl' (\_ current -> current) secondMembership remainingMemberships
+            List.foldl' (\_ current -> current) secondMembership remainingMemberships
           sourceFrom = roundedMembershipPoint firstMembership
           sourceTo = roundedMembershipPoint finalMembership
        in [ SplitOrderNotPreserved
diff --git a/test/native/Moonlight/Triangulation/ExactEmbeddingSpec.hs b/test/native/Moonlight/Triangulation/ExactEmbeddingSpec.hs
--- a/test/native/Moonlight/Triangulation/ExactEmbeddingSpec.hs
+++ b/test/native/Moonlight/Triangulation/ExactEmbeddingSpec.hs
@@ -9,6 +9,7 @@
 import Data.Bits (xor)
 import Data.Foldable (traverse_)
 import Data.List (sort)
+import qualified Data.List as List
 import Data.List.NonEmpty (NonEmpty (..))
 import qualified Data.Map.Strict as Map
 import Data.Word (Word64)
@@ -349,7 +350,7 @@
   checksum <-
     evaluate
       ( force
-          ( foldl'
+          ( List.foldl'
               ( \accumulated value ->
                   accumulated
                     + fromEnum
@@ -584,7 +585,7 @@
   ]
 
 digest :: [SegmentRelation] -> Word64
-digest = foldl' step 14_695_981_039_346_656_037
+digest = List.foldl' step 14_695_981_039_346_656_037
  where
   step :: Word64 -> SegmentRelation -> Word64
   step hash relation =
diff --git a/test/native/Moonlight/Triangulation/NativeSpec.hs b/test/native/Moonlight/Triangulation/NativeSpec.hs
--- a/test/native/Moonlight/Triangulation/NativeSpec.hs
+++ b/test/native/Moonlight/Triangulation/NativeSpec.hs
@@ -20,6 +20,7 @@
 import Control.Monad.ST (runST, stToIO)
 import GHC.Float (castDoubleToWord64)
 import Data.Foldable (toList, traverse_)
+import qualified Data.List as List
 import Data.List.NonEmpty (NonEmpty (..))
 import Data.Maybe (isJust)
 import qualified Data.Map.Strict as Map
@@ -929,9 +930,9 @@
   let plain = buildTriangulation built
       -- Distinct payloads everywhere: a map that permuted its component would
       -- be invisible against uniform defaults.
-      withDirected = foldl' (\t (label, edge) -> setDirectedEdgeData t edge label) plain (zip [100 ..] (directedEdges plain))
-      withUndirected = foldl' (\t (label, edge) -> setUndirectedEdgeData t edge ("u-" <> show label)) withDirected (zip [(0 :: Int) ..] (undirectedEdges withDirected))
-      sample = foldl' (\t (label, face) -> setFaceData t face ("f-" <> show label)) withUndirected (zip [(0 :: Int) ..] (allFaces withUndirected))
+      withDirected = List.foldl' (\t (label, edge) -> setDirectedEdgeData t edge label) plain (zip [100 ..] (directedEdges plain))
+      withUndirected = List.foldl' (\t (label, edge) -> setUndirectedEdgeData t edge ("u-" <> show label)) withDirected (zip [(0 :: Int) ..] (undirectedEdges withDirected))
+      sample = List.foldl' (\t (label, face) -> setFaceData t face ("f-" <> show label)) withUndirected (zip [(0 :: Int) ..] (allFaces withUndirected))
       endpoints ::
         Triangulation mode vertex directed undirected face ->
         [(VertexId, VertexId)]
@@ -1029,9 +1030,9 @@
         ]
   built <- requireRight "payload traversal build" (delaunay defaults payloads)
   let plain = buildTriangulation built
-      withDirected = foldl' (\t (label, edge) -> setDirectedEdgeData t edge label) plain (zip [100 ..] (directedEdges plain))
-      withUndirected = foldl' (\t (label, edge) -> setUndirectedEdgeData t edge ("u-" <> show label)) withDirected (zip [(0 :: Int) ..] (undirectedEdges withDirected))
-      sample = foldl' (\t (label, face) -> setFaceData t face ("f-" <> show label)) withUndirected (zip [(0 :: Int) ..] (allFaces withUndirected))
+      withDirected = List.foldl' (\t (label, edge) -> setDirectedEdgeData t edge label) plain (zip [100 ..] (directedEdges plain))
+      withUndirected = List.foldl' (\t (label, edge) -> setUndirectedEdgeData t edge ("u-" <> show label)) withDirected (zip [(0 :: Int) ..] (undirectedEdges withDirected))
+      sample = List.foldl' (\t (label, face) -> setFaceData t face ("f-" <> show label)) withUndirected (zip [(0 :: Int) ..] (allFaces withUndirected))
 
   -- 'overPayloads' is the traversal under 'Identity', so this is the traversal
   -- identity law. It also says that rebuilding a payload store from its own
@@ -1200,11 +1201,11 @@
   assertEqual "face keys are unique" (length (innerFaces base)) (Map.size faceTable)
 
   let withDirected =
-        foldl' (\t e -> setDirectedEdgeData t e (directedTable Map.! directedKeyOf base e)) base (directedEdges base)
+        List.foldl' (\t e -> setDirectedEdgeData t e (directedTable Map.! directedKeyOf base e)) base (directedEdges base)
       withUndirected =
-        foldl' (\t e -> setUndirectedEdgeData t e (undirectedTable Map.! undirectedKeyOf base e)) withDirected (undirectedEdges base)
+        List.foldl' (\t e -> setUndirectedEdgeData t e (undirectedTable Map.! undirectedKeyOf base e)) withDirected (undirectedEdges base)
       labelled =
-        foldl' (\t f -> setFaceData t f (faceTable Map.! faceKeyOf base f)) withUndirected (innerFaces base)
+        List.foldl' (\t f -> setFaceData t f (faceTable Map.! faceKeyOf base f)) withUndirected (innerFaces base)
   inserted <- requireRight "rewrite identity insert" (insert labelled target)
   let result = insertionTriangulation inserted
   assertValid "rewrite identity result" result
diff --git a/test/serialization/Moonlight/Triangulation/SerializationSpec.hs b/test/serialization/Moonlight/Triangulation/SerializationSpec.hs
--- a/test/serialization/Moonlight/Triangulation/SerializationSpec.hs
+++ b/test/serialization/Moonlight/Triangulation/SerializationSpec.hs
@@ -137,8 +137,14 @@
      , Binary directed
      , Binary undirected
      , Binary face
-     , Eq (Triangulation mode vertex directed undirected face)
-     , Show (Triangulation mode vertex directed undirected face)
+     , Eq vertex
+     , Eq directed
+     , Eq undirected
+     , Eq face
+     , Show vertex
+     , Show directed
+     , Show undirected
+     , Show face
      )
   => String
   -> Triangulation mode vertex directed undirected face