Index: src/main/org/codehaus/groovy/antlr/AntlrParserPlugin.java
===================================================================
--- src/main/org/codehaus/groovy/antlr/AntlrParserPlugin.java	(revision 20068)
+++ src/main/org/codehaus/groovy/antlr/AntlrParserPlugin.java	(revision )
@@ -2929,6 +2949,11 @@
                     "Class definition not expected here. Possible attempt to use inner class. " +
                             "Inner classes not supported, perhaps try using a closure instead.");
         }
+        if (node.getType() == METHOD_DEF) {
+            throw new ASTRuntimeException(node,
+                    "Found a method definition when expecting an expression. Possible attempt to define a method " +
+                            "inside a closure? Define the method outside or use an inner closure.");
+        }
         throw new ASTRuntimeException(node, "Unknown type: " + getTokenName(node));
     }