diff --git a/src/Riok.Mapperly/Descriptors/Enumerables/CollectionInfoBuilder.cs b/src/Riok.Mapperly/Descriptors/Enumerables/CollectionInfoBuilder.cs
index c3708019b1..eb8f9e6b9c 100644
--- a/src/Riok.Mapperly/Descriptors/Enumerables/CollectionInfoBuilder.cs
+++ b/src/Riok.Mapperly/Descriptors/Enumerables/CollectionInfoBuilder.cs
@@ -110,6 +110,11 @@ ITypeSymbol enumeratedType
 
     private static ITypeSymbol? GetEnumeratedType(WellKnownTypes types, ITypeSymbol type)
     {
+        // if type is array return element type
+        // otherwise using the IEnumerable element type can erase the null annotation for external types
+        if (type.IsArrayType())
+            return ((IArrayTypeSymbol)type).ElementType;
+
         if (type.ImplementsGeneric(types.Get(typeof(IEnumerable<>)), out var enumerableIntf))
             return enumerableIntf.TypeArguments[0];