diff --git a/backends/GenerateC.hs b/backends/GenerateC.hs
index 00dd95b..85b4bb5 100644
--- a/backends/GenerateC.hs
+++ b/backends/GenerateC.hs
@@ -185,7 +185,7 @@ cgenTopLevel headerName s
               isBodySpec (A.Specification _ n sp)
                 = A.nameName n `notElem` (csOriginalTopLevelProcs cs)
 
-          tellToHeader (nameString $ A.Name emptyMeta $ dropPath headerName)
+          tellToHeader (mungeToC $ dropPath headerName)
             $ sequence_ $ map (call genForwardDeclaration True)
                                        (reverse $ listifyDepth isHeaderSpec s)
 
@@ -274,6 +274,10 @@ cgenTopLevel headerName s
     
     mungeExternalName (_:cs) = [if c == '.' then '_' else c | c <- cs]
 
+    mungeToC cs = [if c `elem` valid then c else '_' | c <- cs]
+      where
+        valid = ['a'..'z'] ++ ['A'..'Z'] ++ ['0'..'9'] ++ "_"
+
     -- | Allocate a TLP channel handler process, and return the function that
     -- implements it.
     genTLPHandler :: (Maybe A.Direction, TLPChannel) -> String -> String -> String -> CGen String