diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -30,4 +30,8 @@
 
 ## 0.6.0.1 -- 2024-01-14
 
-* Correct bug in completeDiagram.
+* Correct bug in completeDiagram.
+
+## 0.6.0.2 -- 2024-01-22
+
+* Bug fix in checkNaturalTransformation.
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:            0.6.0.1
+version:            0.6.0.2
 
 -- A short (one-line) description of the package.
 synopsis: Finite categories and usual categorical constructions on them.
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
@@ -376,6 +376,8 @@
     -- | A datatype to represent a malformation of a 'NaturalTransformation'.
     data NaturalTransformationError c1 m1 o1 c2 m2 o2 = IncompatibleFunctorsSource{sourceCat :: c1, targetCat :: c1} -- ^ The source and target functors don't have the same source category.
                                                       | IncompatibleFunctorsTarget{sourceCat2 :: c2, targetCat2 :: c2} -- ^ The source and target functors don't have the same target category.
+                                                      | WrongComponentSource{faultyComponent1 :: m2, correctSource :: o1} -- ^ The source of a component is not the image of the indexing object by the source functor. 
+                                                      | WrongComponentTarget{faultyComponent2 :: m2, correctTarget :: o1} -- ^ The target of a component is not the image of the indexing object by the target functor. 
                                                       | NotTotal{domainNat :: Set o1, objectsCat :: Set o1} -- ^ The mapping from objects to morphisms is not total.
                                                       | NaturalityFail{originalMorphism :: m1} -- ^ A morphism does not close a commutative square.
                                                       deriving (Eq, Show, Generic, PrettyPrint, Simplifiable)
@@ -389,12 +391,16 @@
         | incompatibleFunctorsSource = Just IncompatibleFunctorsSource{sourceCat=(src.source $ nt), targetCat=(src.target $ nt)}
         | incompatibleFunctorsTarget = Just IncompatibleFunctorsTarget{sourceCat2=(tgt.source $ nt), targetCat2=(tgt.target $ nt)}
         | notTotal = Just NotTotal{domainNat = (domain.components $ nt), objectsCat = (ob.src.source $ nt)}
+        | (not.(Set.null)) wrongSource = Just WrongComponentSource{faultyComponent1 = fst $ anElement wrongSource, correctSource = snd $ anElement wrongSource}
+        | (not.(Set.null)) wrongTarget = Just WrongComponentTarget{faultyComponent2 = fst $ anElement wrongTarget, correctTarget = snd $ anElement wrongTarget}
         | (not.(Set.null)) naturalityFail = Just NaturalityFail{originalMorphism = anElement naturalityFail}
         | otherwise = Nothing
         where
             incompatibleFunctorsSource = (src.source $ nt) /= (src.target $ nt)
             incompatibleFunctorsTarget = (tgt.source $ nt) /= (tgt.target $ nt)  
             notTotal = (domain.components $ nt) /= (ob.src.source $ nt)
+            wrongSource = [((nt =>$ i),i) | i <- (ob.src.source $ nt), (source nt) ->$ i /= source (nt =>$ i)]
+            wrongTarget = [((nt =>$ i),i) | i <- (ob.src.source $ nt), (target nt) ->$ i /= target (nt =>$ i)]
             naturalityFail = [f | f <- (arrows.src.source $ nt), (target nt ->£ f) @ (nt =>$ (source f)) /= (nt =>$ (target f)) @ (source nt ->£ f)]
     
     -- | The smart constructor of 'NaturalTransformation'. Checks wether the structure is correct.