diff --git a/Cabal/Distribution/InstalledPackageInfo.hs b/Cabal/Distribution/InstalledPackageInfo.hs
index 94d4ade3198..08e197bc2e4 100644
--- a/Cabal/Distribution/InstalledPackageInfo.hs
+++ b/Cabal/Distribution/InstalledPackageInfo.hs
@@ -30,7 +30,7 @@ module Distribution.InstalledPackageInfo (
         InstalledPackageInfo(..),
         installedComponentId,
         installedPackageId,
-        OriginalModule(..), ExposedModule(..),
+        ExposedModule(..),
         ParseResult(..), PError(..), PWarning,
         emptyInstalledPackageInfo,
         parseInstalledPackageInfo,
@@ -162,29 +162,13 @@ emptyInstalledPackageInfo
 -- -----------------------------------------------------------------------------
 -- Exposed modules
 
-data OriginalModule
-   = OriginalModule {
-       originalPackageId  :: UnitId,
-       originalModuleName :: ModuleName
-     }
-  deriving (Generic, Eq, Read, Show)
-
 data ExposedModule
    = ExposedModule {
        exposedName      :: ModuleName,
-       exposedReexport  :: Maybe OriginalModule
+       exposedReexport  :: Maybe Module
      }
   deriving (Eq, Generic, Read, Show)
 
-instance Text OriginalModule where
-    disp (OriginalModule ipi m) =
-        disp ipi <> Disp.char ':' <> disp m
-    parse = do
-        ipi <- parse
-        _ <- Parse.char ':'
-        m <- parse
-        return (OriginalModule ipi m)
-
 instance Text ExposedModule where
     disp (ExposedModule m reexport) =
         Disp.sep [ disp m
@@ -202,8 +186,6 @@ instance Text ExposedModule where
         return (ExposedModule m reexport)
 
 
-instance Binary OriginalModule
-
 instance Binary ExposedModule
 
 -- To maintain backwards-compatibility, we accept both comma/non-comma
diff --git a/Cabal/Distribution/Package.hs b/Cabal/Distribution/Package.hs
index 7f9628f3ea9..1fec1c8c0c4 100644
--- a/Cabal/Distribution/Package.hs
+++ b/Cabal/Distribution/Package.hs
@@ -30,6 +30,9 @@ module Distribution.Package (
         getHSLibraryName,
         InstalledPackageId, -- backwards compat
 
+        -- * Modules
+        Module(..),
+
         -- * ABI hash
         AbiHash(..),
 
@@ -55,6 +58,7 @@ import qualified Text.PrettyPrint as Disp
 import Distribution.Compat.ReadP
 import Distribution.Compat.Binary
 import Distribution.Text
+import Distribution.ModuleName
 
 import Control.DeepSeq (NFData(..))
 import qualified Data.Char as Char
@@ -111,9 +115,32 @@ instance Text PackageIdentifier where
 instance NFData PackageIdentifier where
     rnf (PackageIdentifier name version) = rnf name `seq` rnf version
 
--- ------------------------------------------------------------
--- * Component Source Hash
--- ------------------------------------------------------------
+-- | A module identity uniquely identifies a Haskell module by
+-- qualifying a 'ModuleName' with the 'UnitId' which defined
+-- it.  This type distinguishes between two packages
+-- which provide a module with the same name, or a module
+-- from the same package compiled with different dependencies.
+-- There are a few cases where Cabal needs to know about
+-- module identities, e.g., when writing out reexported modules in
+-- the 'InstalledPackageInfo'.
+data Module =
+    Module { moduleUnitId :: UnitId,
+             moduleName :: ModuleName }
+    deriving (Generic, Read, Show, Eq, Ord, Typeable, Data)
+
+instance Binary Module
+
+instance Text Module where
+    disp (Module uid mod_name) =
+        disp uid <> Disp.text ":" <> disp mod_name
+    parse = do
+        uid <- parse
+        _ <- Parse.char ':'
+        mod_name <- parse
+        return (Module uid mod_name)
+
+instance NFData Module where
+    rnf (Module uid mod_name) = rnf uid `seq` rnf mod_name
 
 -- | A 'ComponentId' uniquely identifies the transitive source
 -- code closure of a component.  For non-Backpack components, it also
diff --git a/Cabal/Distribution/Simple/Configure.hs b/Cabal/Distribution/Simple/Configure.hs
index a0492aaa457..86a74a94b75 100644
--- a/Cabal/Distribution/Simple/Configure.hs
+++ b/Cabal/Distribution/Simple/Configure.hs
@@ -1740,8 +1740,8 @@ resolveModuleReexports installedPackages srcpkgid key externalPkgDeps lib =
         , let exportingPackageName = packageName srcpkgid
               definingModuleName   = visibleModuleName
               definingPackageId    = key
-              originalModule = Installed.OriginalModule definingPackageId
-                                                        definingModuleName
+              originalModule = Module definingPackageId
+                                      definingModuleName
               exposedModule  = Installed.ExposedModule visibleModuleName
                                                        (Just originalModule)
         ]
@@ -1758,7 +1758,7 @@ resolveModuleReexports installedPackages srcpkgid key externalPkgDeps lib =
         -- In this case the reexport will point to this package.
             Nothing -> return exposedModule {
               Installed.exposedReexport =
-                 Just (Installed.OriginalModule
+                 Just (Module
                        (Installed.installedUnitId pkg)
                        (Installed.exposedName exposedModule)) }
         -- On the other hand, a visible module might actually be itself
diff --git a/Cabal/Distribution/Simple/PackageIndex.hs b/Cabal/Distribution/Simple/PackageIndex.hs
index 04e3367205f..9ad1249e7aa 100644
--- a/Cabal/Distribution/Simple/PackageIndex.hs
+++ b/Cabal/Distribution/Simple/PackageIndex.hs
@@ -614,8 +614,8 @@ moduleNameIndex index =
     IPI.ExposedModule m reexport <- IPI.exposedModules pkg
     case reexport of
         Nothing -> return (m, [pkg])
-        Just (IPI.OriginalModule _ m') | m == m'   -> []
-                                       | otherwise -> return (m', [pkg])
+        Just (Module _ m') | m == m'   -> []
+                           | otherwise -> return (m', [pkg])
         -- The heuristic is this: we want to prefer the original package
         -- which originally exported a module.  However, if a reexport
         -- also *renamed* the module (m /= m'), then we have to use the