diff --git a/src/back/CCode/Main.hs b/src/back/CCode/Main.hs
index 73073b6d3..e288fa5b9 100644
--- a/src/back/CCode/Main.hs
+++ b/src/back/CCode/Main.hs
@@ -99,3 +99,4 @@ data CCode a where
     String       :: String -> CCode Expr
     Double       :: Double -> CCode Expr
     Comm         :: String -> CCode a
+    Annotated    :: String -> CCode a -> CCode a
diff --git a/src/back/CCode/PrettyCCode.hs b/src/back/CCode/PrettyCCode.hs
index 06af5447b..a33133e1e 100644
--- a/src/back/CCode/PrettyCCode.hs
+++ b/src/back/CCode/PrettyCCode.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE GADTs,FlexibleContexts #-}
+{-# OPTIONS_GHC -fwarn-incomplete-patterns #-}
 
 {-|
 Converting CCode (see "CCode.Main") to C source.
@@ -109,6 +110,8 @@ pp' (Int n) = tshow n
 pp' (String s) = tshow s
 pp' (Double d) = tshow d
 pp' (Comm s) = text ("/* "++s++" */")
+--Annotated :: CCode a -> String -> CCode a
+pp' (Annotated s ccode) = pp' ccode <+> pp' (Comm s)
 
 commaList :: [CCode a] -> Doc
 commaList l = hcat $ intersperse (text ", ") $ map pp' l
diff --git a/src/back/CodeGen/ClassDecl.hs b/src/back/CodeGen/ClassDecl.hs
index ca2828e36..a9b66e0c1 100644
--- a/src/back/CodeGen/ClassDecl.hs
+++ b/src/back/CodeGen/ClassDecl.hs
@@ -160,9 +160,10 @@ translateActiveClass cdecl@(A.Class{A.cname, A.fields, A.methods}) =
              -- explode _enc__Foo_bar_msg_t struct into variable names
              method_unpack_arguments :: A.MethodDecl -> CCode Ty -> [CCode Stat]
              method_unpack_arguments mdecl msg_type_name = 
-               map unpack (A.mparams mdecl)
+               zipWith unpack (A.mparams mdecl) [1..]
                  where
-                   unpack A.Param{A.pname, A.ptype} = (Assign (Decl (translate ptype, (Var $ show pname))) ((Cast (msg_type_name) (Var "_m")) `Arrow` (Nam $ show pname)))
+                   unpack :: A.ParamDecl -> Int -> CCode Stat
+                   unpack A.Param{A.pname, A.ptype} n = (Assign (Decl (translate ptype, (Var $ show pname))) ((Cast (msg_type_name) (Var "_m")) `Arrow` (Nam $ "f"++show n)))
 
              mthd_dispatch_clause mdecl@(A.Method{A.mname, A.mparams, A.mtype})  =
                 (method_msg_name cname mname,
diff --git a/src/back/CodeGen/Header.hs b/src/back/CodeGen/Header.hs
index cd56a0555..3fa319a78 100644
--- a/src/back/CodeGen/Header.hs
+++ b/src/back/CodeGen/Header.hs
@@ -90,8 +90,8 @@ generate_header A.Program{A.etl = A.EmbedTL{A.etlheader}, A.functions, A.classes
             pony_msg_t_impl :: A.MethodDecl -> CCode Toplevel
             pony_msg_t_impl mdecl =
               let argrttys = map (translate . A.getType) (A.mparams mdecl)
-                  argnames = map (Var . show . A.pname)  (A.mparams mdecl)
-                  argspecs = zip argrttys argnames :: [CVarSpec]
+                  argnames_w_comments = zipWith (\n name -> (Annotated (show name) (Var ("f"++show n)))) ([1..]:: [Int]) (map A.pname $ A.mparams mdecl)
+                  argspecs = zip argrttys argnames_w_comments :: [CVarSpec]
                   encoremsgtspec = (enc_msg_t, Var "msg")
                   encoremsgtspec_oneway = (enc_oneway_msg_t, Var "msg")
                   nameprefix = "_enc__"++ (show (A.cname cdecl))