diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Revision history for random-cycle
 
+## 0.1.2.0 -- 2023-11-19
+
+* Fixes a bug in 'uniformCyclePartitionThin'.
+
 ## 0.1.1.0 -- 2023-05-07
 
 * Adds Sattolo's algorithm to sample full cycles.
diff --git a/random-cycle.cabal b/random-cycle.cabal
--- a/random-cycle.cabal
+++ b/random-cycle.cabal
@@ -1,6 +1,6 @@
 cabal-version:      2.4
 name:               random-cycle
-version:            0.1.1.0
+version:            0.1.2.0
 synopsis: Uniform draws of partitions and cycle-partitions, with thinning.
 
 description: 
diff --git a/src/RandomCycle/Vector/Cycle.hs b/src/RandomCycle/Vector/Cycle.hs
--- a/src/RandomCycle/Vector/Cycle.hs
+++ b/src/RandomCycle/Vector/Cycle.hs
@@ -4,7 +4,7 @@
 -- Import 'RandomCycle.Vector' instead.
 module RandomCycle.Vector.Cycle where
 
-import Control.Monad (when)
+import Control.Monad (unless)
 import Control.Monad.Primitive (PrimMonad, PrimState, liftPrim)
 import Data.STRef
 import qualified Data.Vector as V
@@ -29,21 +29,19 @@
 uniformCyclePartitionThinM chk maxit r v gen = do
   maxitVal <- liftPrim $ readSTRef maxit
 
-  when (maxitVal <= 0) (pure ())
-
-  uniformShuffleM v gen
-  -- TODO: Repeated calls to freeze, indexed
-  -- a possible opportunity for optimization,
-  -- e.g. with imap or a check that takes 'chk'
-  -- reference and shortcircuits.
-  vVal <- V.freeze v
-  if V.all r (V.indexed vVal)
-    then do
-      liftPrim $ modifySTRef' chk (const True)
-    else do
-      liftPrim $ modifySTRef' maxit (\x -> x - 1)
-      uniformCyclePartitionThinM chk maxit r v gen
-  pure ()
+  unless (maxitVal <= 0) $ do
+    uniformShuffleM v gen
+    -- TODO: Repeated calls to freeze, indexed
+    -- a possible opportunity for optimization,
+    -- e.g. with imap or a check that takes 'chk'
+    -- reference and shortcircuits.
+    vVal <- V.freeze v
+    if V.all r (V.indexed vVal)
+      then do
+        liftPrim $ modifySTRef' chk (const True)
+      else do
+        liftPrim $ modifySTRef' maxit (\x -> x - 1)
+        uniformCyclePartitionThinM chk maxit r v gen
 
 -- | Internal. Helper for'uniformCycle'. Caller's responsibility to ensure
 -- first input is the length of the vector, and that i ranges over @[0..n-2]@.