diff --git a/copilot-cbmc.cabal b/copilot-cbmc.cabal
--- a/copilot-cbmc.cabal
+++ b/copilot-cbmc.cabal
@@ -1,6 +1,6 @@
 cabal-version             : >= 1.10
 name                      : copilot-cbmc
-version                   : 2.1.1
+version                   : 2.1.2
 synopsis                  : Copilot interface to a C model-checker.
 description               :
   Depends on CBMC <http://www.cprover.org/cbmc/>.  Generates a driver to prove
@@ -37,7 +37,7 @@
   ghc-options             : -Wall -fwarn-tabs
   ghc-prof-options        : -auto-all -caf-all
 
-  build-depends           : base >= 4.0 && <= 5.0
+  build-depends           : base >= 4.0 && < 5.0
                           , bytestring >= 0.9
                           , copilot-core >= 0.2.4
                           , directory >= 1.1
diff --git a/src/Copilot/Tools/CBMC.hs b/src/Copilot/Tools/CBMC.hs
--- a/src/Copilot/Tools/CBMC.hs
+++ b/src/Copilot/Tools/CBMC.hs
@@ -3,6 +3,7 @@
 --------------------------------------------------------------------------------
 
 {-# LANGUAGE GADTs #-}
+{-# LANGUAGE Rank2Types #-}
 
 module Copilot.Tools.CBMC 
   ( Params (..)
@@ -148,18 +149,18 @@
 --------------------------------------------------------------------------------
 
 typeSpec :: UType -> Doc
-typeSpec UType { uTypeType = t } = text (typeSpec' t)
-  where
-  typeSpec' Bool   = "bool"
-  typeSpec' Int8   = "int8_t"
-  typeSpec' Int16  = "int16_t"
-  typeSpec' Int32  = "int32_t"
-  typeSpec' Int64  = "int64_t"
-  typeSpec' Word8  = "uint8_t"
-  typeSpec' Word16 = "uint16_t"
-  typeSpec' Word32 = "uint32_t"
-  typeSpec' Word64 = "uint64_t"
-  typeSpec' Float  = "float"
-  typeSpec' Double = "double"
+typeSpec UType { uTypeType = t } = text $
+  case t of
+    Bool   -> "bool"
+    Int8   -> "int8_t"
+    Int16  -> "int16_t"
+    Int32  -> "int32_t"
+    Int64  -> "int64_t"
+    Word8  -> "uint8_t"
+    Word16 -> "uint16_t"
+    Word32 -> "uint32_t"
+    Word64 -> "uint64_t"
+    Float  -> "float"
+    Double -> "double"
 
 --------------------------------------------------------------------------------