diff --git a/uppsrc/CppBase/CppBase.h b/uppsrc/CppBase/CppBase.h
index a6611d62b..53a86d271 100644
--- a/uppsrc/CppBase/CppBase.h
+++ b/uppsrc/CppBase/CppBase.h
@@ -20,9 +20,9 @@ const VectorMap<String, String>& GetNamespaceMacros();
 const Index<String>&             GetNamespaceEndMacros();
 
 struct CppMacro : Moveable<CppMacro> {
-
 	String        param;
 	String        body;
+	byte          md5[16];
 	
 	String Define(const char *s);
 	void   SetUndef()                { body = "\x7f"; }
diff --git a/uppsrc/CppBase/macro.cpp b/uppsrc/CppBase/macro.cpp
index 0c2b05ee3..161b33ddf 100644
--- a/uppsrc/CppBase/macro.cpp
+++ b/uppsrc/CppBase/macro.cpp
@@ -36,6 +36,10 @@ String CppMacro::Define(const char *s)
 		while(!p.IsEof() && !p.IsChar2('/', '/'))
 			p.SkipTerm();
 		body = String(b, p.GetPtr());
+		Md5Stream m;
+		m.Put(param);
+		m.Put(body);
+		m.Finish(md5);
 	}
 	catch(CParser::Error) {
 		return Null;