diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -62,4 +62,8 @@
 
 ## 0.6.5.0 -- 2024-05-16
 
-* Changes to simplification of CGMorphism
+* Changes to simplification of CGMorphism
+
+## 0.6.5.1 -- 2024-05-31
+
+* Relax container version bounds
diff --git a/FiniteCategories.cabal b/FiniteCategories.cabal
--- a/FiniteCategories.cabal
+++ b/FiniteCategories.cabal
@@ -14,7 +14,7 @@
 -- PVP summary:      +-+------- breaking API changes
 --                   | | +----- non-breaking API additions
 --                   | | | +--- code changes with no API change
-version:             0.6.5.0
+version:             0.6.5.1
 
 -- A short (one-line) description of the package.
 synopsis: Finite categories and usual categorical constructions on them.
@@ -133,7 +133,7 @@
     build-depends:      base             >= 4 && < 5,
                         random           >= 1.2.1 && < 1.3,
                         WeakSets         >= 1.6.1.0 && < 1.7,
-                        containers       >= 0.6.6.0 && < 0.7,
+                        containers       >= 0.6.0.0 && < 0.7,
                         text             >= 1.0 && < 2.2,
                         filepath         >= 1.4.100.1 && < 1.5,
                         directory        >= 1.3.8.1 && < 1.4,
@@ -163,7 +163,7 @@
                         base             >= 4 && < 5,
                         random           >= 1.2.1 && < 2,
                         WeakSets         >= 1.6.1 && < 1.7,
-                        containers       >= 0.6.6.0 && < 0.7,
+                        containers       >= 0.6.0.0 && < 0.7,
                         text             >= 1.0 && < 2.2,
                         filepath         >= 1.4.100.1 && < 1.5,
                         directory        >= 1.3.8.1 && < 1.4,
diff --git a/src/Math/Categories/FunctorCategory.hs b/src/Math/Categories/FunctorCategory.hs
--- a/src/Math/Categories/FunctorCategory.hs
+++ b/src/Math/Categories/FunctorCategory.hs
@@ -215,7 +215,7 @@
                       Diagram c1 m1 o1 c2 m2 o2 -> Maybe (DiagramError c1 m1 o1 c2 m2 o2)
     checkDiagram d@Diagram{src=s,tgt=t,omap=om,mmap=fm}
         | domain om /= ob s = Just WrongDomainObjects{srcObjs = ob s, domainObjs = domain om}
-        | not $ (genArrows s) `isIncludedIn` (domain fm) = Just WrongDomainMorphisms{srcMorphs = arrows s, domainMorphs = domain fm}
+        | not $ (genArrows s) `isIncludedIn` (domain fm) = Just WrongDomainMorphisms{srcMorphs = genArrows s, domainMorphs = domain fm}
         | not.(Set.null) $ tear = Just TornMorphism{f = anElement tear, fImage = d ->£ (anElement tear)}
         | not.(Set.null) $ imId = Just IdentityNotPreserved{originalId = identity s (anElement imId), imageId = d ->£ (identity s (anElement imId))}
         | otherwise = Nothing