diff --git a/src/main/java/org/codehaus/groovy/transform/stc/StaticTypeCheckingVisitor.java b/src/main/java/org/codehaus/groovy/transform/stc/StaticTypeCheckingVisitor.java
index abbc6331ee8..681cf9f41a4 100644
--- a/src/main/java/org/codehaus/groovy/transform/stc/StaticTypeCheckingVisitor.java
+++ b/src/main/java/org/codehaus/groovy/transform/stc/StaticTypeCheckingVisitor.java
@@ -3069,7 +3069,7 @@ protected void visitMethodCallArguments(final ClassNode receiver, final Argument
                             expression.putNodeMetaData(PARAMETER_TYPE, lambda.getNodeMetaData(PARAMETER_TYPE));
                             expression.putNodeMetaData(CLOSURE_ARGUMENTS, lambda.getNodeMetaData(CLOSURE_ARGUMENTS));
                         } else {
-                            addError("The argument is a method reference, but the parameter type is not a functional interface", expression);
+                            addStaticTypeError("Argument is a method reference, but parameter type '" + prettyPrintTypeName(targetType) + "' is not a functional interface", expression);
                         }
                     }
                 }
@@ -3500,7 +3500,7 @@ private void checkClosureWithDelegatesTo(final ClassNode receiver, final MethodN
                             resolveGenericsFromTypeHint(receiver, arguments, mn, resolved);
                             expression.putNodeMetaData(DELEGATION_METADATA, newDelegationMetadata(resolved[0], stInt));
                         } else {
-                            addStaticTypeError("Incorrect type hint found in method " + (mn), type);
+                            addStaticTypeError("Incorrect type hint found in method " + mn, type);
                         }
                     }
                 } else {
@@ -5925,12 +5925,8 @@ public void addError(final String msg, final ASTNode node) {
     protected void addStaticTypeError(final String msg, final ASTNode node) {
         if (node.getColumnNumber() > 0 && node.getLineNumber() > 0) {
             addError(StaticTypesTransformation.STATIC_ERROR_PREFIX + msg, node);
-        } else {
-            if (DEBUG_GENERATED_CODE) {
-                addError(StaticTypesTransformation.STATIC_ERROR_PREFIX + "Error in generated code [" + node.getText() + "] - " + msg, node);
-            }
-            // ignore errors which are related to unknown source locations
-            // because they are likely related to generated code
+        } else if (DEBUG_GENERATED_CODE) { // if not debug, ignore errors which are related to unknown source locations (generated code)
+            addError(StaticTypesTransformation.STATIC_ERROR_PREFIX + "Error in generated code [" + node.getText() + "] - " + msg, node);
         }
     }
 
diff --git a/src/test/groovy/transform/stc/MethodReferenceTest.groovy b/src/test/groovy/transform/stc/MethodReferenceTest.groovy
index 8c1bdc7b641..22539d12c91 100644
--- a/src/test/groovy/transform/stc/MethodReferenceTest.groovy
+++ b/src/test/groovy/transform/stc/MethodReferenceTest.groovy
@@ -1456,7 +1456,7 @@ final class MethodReferenceTest {
                 baz(this::foo) // not yet supported!
             }
         '''
-        assert err =~ /The argument is a method reference, but the parameter type is not a functional interface/
+        assert err =~ /Argument is a method reference, but parameter type 'java.lang.Object' is not a functional interface/
     }
 
     @Test // GROOVY-10336
@@ -1473,7 +1473,27 @@ final class MethodReferenceTest {
                 }
             }
         '''
-        assert err =~ /The argument is a method reference, but the parameter type is not a functional interface/
+        assert err =~ /Argument is a method reference, but parameter type 'java.lang.Object' is not a functional interface/
+    }
+
+    @Test // GROOVY-10979
+    void testNotFunctionalInterface3() {
+        def err = shouldFail shell, '''
+            Integer m(String x) {
+                return 1
+            }
+            @CompileStatic
+            void test() {
+                java.util.stream.Stream<Number>                                          x = null
+                BiFunction<Function<String, Integer>, Number, Function<String, Integer>> y = null
+                BinaryOperator<Function<String, Integer>>                                z = null
+                // reduce number(s) to string-to-integer functions
+                x.<Function<String, Integer>>reduce(this::m, y, z)
+                x.reduce(this::m, y, z)
+                x.reduce((s) -> 1, y, z)
+            }
+        '''
+        assert err =~ /Argument is a method reference, but parameter type 'U' is not a functional interface/
     }
 
     @Test // GROOVY-11254