diff --git a/codegen/config/binder.go b/codegen/config/binder.go
index 41c3efef269..bfd12bbce15 100644
--- a/codegen/config/binder.go
+++ b/codegen/config/binder.go
@@ -349,7 +349,7 @@ func (b *Binder) TypeReference(schemaType *ast.Type, bindTarget types.Type) (ret
 		} else if hasMethod(obj.Type(), "MarshalGQL") && hasMethod(obj.Type(), "UnmarshalGQL") {
 			ref.GO = obj.Type()
 			ref.IsMarshaler = true
-		} else if underlying := basicUnderlying(obj.Type()); underlying != nil && underlying.Kind() == types.String {
+		} else if underlying := basicUnderlying(obj.Type()); def.IsLeafType() && underlying != nil && underlying.Kind() == types.String {
 			// Special case for named types wrapping strings. Used by default enum implementations.
 
 			ref.GO = obj.Type()
diff --git a/codegen/testserver/generated.go b/codegen/testserver/generated.go
index 39f45f0aa79..a3f26e4f569 100644
--- a/codegen/testserver/generated.go
+++ b/codegen/testserver/generated.go
@@ -8216,13 +8216,7 @@ func (ec *executionContext) marshalNPrimitive2ᚕgithubᚗcomᚋ99designsᚋgqlg
 }
 
 func (ec *executionContext) marshalNPrimitiveString2githubᚗcomᚋ99designsᚋgqlgenᚋcodegenᚋtestserverᚐPrimitiveString(ctx context.Context, sel ast.SelectionSet, v PrimitiveString) graphql.Marshaler {
-	res := graphql.MarshalString(string(v))
-	if res == graphql.Null {
-		if !ec.HasError(graphql.GetResolverContext(ctx)) {
-			ec.Errorf(ctx, "must not be null")
-		}
-	}
-	return res
+	return ec._PrimitiveString(ctx, sel, &v)
 }
 
 func (ec *executionContext) marshalNPrimitiveString2ᚕgithubᚗcomᚋ99designsᚋgqlgenᚋcodegenᚋtestserverᚐPrimitiveString(ctx context.Context, sel ast.SelectionSet, v []PrimitiveString) graphql.Marshaler {
diff --git a/codegen/testserver/primitive_objects_test.go b/codegen/testserver/primitive_objects_test.go
index f3b46c2bb88..6ceef5c8f7d 100644
--- a/codegen/testserver/primitive_objects_test.go
+++ b/codegen/testserver/primitive_objects_test.go
@@ -61,7 +61,7 @@ func TestPrimitiveStringObjects(t *testing.T) {
 			PrimitiveStringObject []struct {
 				Value   string
 				Doubled string
-				Len int
+				Len     int
 			}
 		}
 		c.MustPost(`query { primitiveStringObject { value, doubled, len } }`, &resp)