diff --git a/CHANGELOG b/CHANGELOG
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -1,3 +1,8 @@
+2022-11-07
+        * Version bump (3.12). (#389)
+        * Removed deprecated flag from cabal file. (#380)
+        * Generate type declarations in separate header file. (#373)
+
 2022-09-07
         * Version bump (3.11). (#376)
         * Update to support language-c99-0.2.0. (#371)
diff --git a/copilot-c99.cabal b/copilot-c99.cabal
--- a/copilot-c99.cabal
+++ b/copilot-c99.cabal
@@ -1,6 +1,6 @@
 cabal-version             : >= 1.10
 name                      : copilot-c99
-version                   : 3.11
+version                   : 3.12
 synopsis                  : A compiler for Copilot targeting C99.
 description               :
   This package is a back-end from Copilot to C.
@@ -38,18 +38,14 @@
   default-language        : Haskell2010
   hs-source-dirs          : src
 
-  -- The following -Wno-deprecations is temprary and related to issue
-  -- https://github.com/Copilot-Language/copilot/issues/237
-  -- It should be removed in a future version, when this library hides
-  -- internal modules.
-  ghc-options             : -Wall -Wno-deprecations
+  ghc-options             : -Wall
   build-depends           : base                >= 4.9 && < 5
                           , directory           >= 1.3 && < 1.4
                           , filepath            >= 1.4 && < 1.5
                           , mtl                 >= 2.2 && < 2.4
                           , pretty              >= 1.1 && < 1.2
 
-                          , copilot-core        >= 3.11  && < 3.12
+                          , copilot-core        >= 3.12  && < 3.13
                           , language-c99        >= 0.2.0 && < 0.3
                           , language-c99-simple >= 0.2.2 && < 0.3
 
diff --git a/src/Copilot/Compile/C99/Compile.hs b/src/Copilot/Compile/C99/Compile.hs
--- a/src/Copilot/Compile/C99/Compile.hs
+++ b/src/Copilot/Compile/C99/Compile.hs
@@ -38,6 +38,7 @@
   | otherwise
   = do let cfile = render $ pretty $ C.translate $ compilec cSettings spec
            hfile = render $ pretty $ C.translate $ compileh cSettings spec
+           typeDeclnsFile = safeCRender $ compileTypeDeclns cSettings spec
 
            cmacros = unlines [ "#include <stdint.h>"
                              , "#include <stdbool.h>"
@@ -45,6 +46,7 @@
                              , "#include <stdlib.h>"
                              , "#include <math.h>"
                              , ""
+                             , "#include \"" ++ prefix ++ "_types.h\""
                              , "#include \"" ++ prefix ++ ".h\""
                              , ""
                              ]
@@ -53,6 +55,7 @@
        createDirectoryIfMissing True dir
        writeFile (dir </> prefix ++ ".c") $ cmacros ++ cfile
        writeFile (dir </> prefix ++ ".h") hfile
+       writeFile (dir </> prefix ++ "_types.h") typeDeclnsFile
 
 -- | Compile a specification to a .h and a .c file.
 --
@@ -74,21 +77,10 @@
     streams  = specStreams spec
     triggers = specTriggers spec
     exts     = gatherexts streams triggers
-    exprs    = gatherexprs streams triggers
 
-    declns = mkstructdeclns exprs ++ mkexts exts ++ mkglobals streams
+    declns = mkexts exts ++ mkglobals streams
     funs   = genfuns streams triggers ++ [mkstep cSettings streams triggers exts]
 
-    -- Write struct datatypes
-    mkstructdeclns :: [UExpr] -> [C.Decln]
-    mkstructdeclns es = catMaybes $ map mkdecln utypes
-      where
-        mkdecln (UType ty) = case ty of
-          Struct x -> Just $ mkstructdecln ty
-          _        -> Nothing
-
-        utypes = nub $ concatMap (\(UExpr _ e) -> exprtypes e) es
-
     -- Make declarations for copies of external variables.
     mkexts :: [External] -> [C.Decln]
     mkexts exts = map mkextcpydecln exts
@@ -171,3 +163,32 @@
     stepdecln :: C.Decln
     stepdecln = C.FunDecln Nothing (C.TypeSpec C.Void)
                     (cSettingsStepFunctionName cSettings) []
+
+-- | Generate a C translation unit that contains all type declarations needed
+-- by the Copilot specification.
+compileTypeDeclns :: CSettings -> Spec -> C.TransUnit
+compileTypeDeclns _cSettings spec = C.TransUnit declns []
+  where
+    declns = mkTypeDeclns exprs
+
+    exprs    = gatherexprs streams triggers
+    streams  = specStreams spec
+    triggers = specTriggers spec
+
+    -- Generate type declarations.
+    mkTypeDeclns :: [UExpr] -> [C.Decln]
+    mkTypeDeclns es = catMaybes $ map mkTypeDecln uTypes
+      where
+        uTypes = nub $ concatMap (\(UExpr _ e) -> exprtypes e) es
+
+        mkTypeDecln (UType ty) = case ty of
+          Struct _ -> Just $ mkstructdecln ty
+          _        -> Nothing
+
+-- * Auxiliary definitions
+
+-- | Render a C.TransUnit to a String, accounting for the case in which the
+-- translation unit is empty.
+safeCRender :: C.TransUnit -> String
+safeCRender (C.TransUnit [] []) = ""
+safeCRender transUnit           = render $ pretty $ C.translate transUnit