diff --git a/backends/BackendPasses.hs b/backends/BackendPasses.hs
index dd61d40..576fc01 100644
--- a/backends/BackendPasses.hs
+++ b/backends/BackendPasses.hs
@@ -330,7 +330,13 @@ addSizesFormalParameters :: Pass
 addSizesFormalParameters = occamOnlyPass "Add array-size arrays to PROC headers"
   (prereq ++ [Prop.arraySizesDeclared])
   []
-  (applyDepthM doSpecification)
+  (\t -> do t' <- applyDepthM doSpecification t
+            cs <- getCompState
+            sequence_ [doSpecification $ A.Specification emptyMeta (A.Name emptyMeta n)
+                         (A.Proc emptyMeta (A.PlainSpec, A.PlainRec)
+                           fs (A.Skip emptyMeta))
+                      | (n, fs) <- csExternals cs]
+            return t')
   where
     doSpecification :: A.Specification -> PassM A.Specification
     doSpecification (A.Specification m n (A.Proc m' sm args body))
diff --git a/backends/GenerateC.hs b/backends/GenerateC.hs
index 9119c7f..9fcb200 100644
--- a/backends/GenerateC.hs
+++ b/backends/GenerateC.hs
@@ -2041,8 +2041,12 @@ cgenProcCall n as
             (A.Recursive, _) ->
               let m = A.nameMeta n
               in call genPar A.PlainPar $ A.Only m $ A.ProcCall m n as
-            (_, Just fs) ->
+            (_, Just _) ->
                  do tell ["{int args_plus_blank[] = {0"]
+                    -- We don't use the formals in externals because they won't
+                    -- have had array sizes added:
+                    (A.Proc _ _ fs _) <- specTypeOfName n
+                    liftIO $ putStrLn $ show (fs, as)
                     call genActuals fs as
                     tell ["};"]
                     let (_:cs) = A.nameName n