3 files changed, 11 insertions, 11 deletions
diff --git a/compiler/basicTypes/Module.hs b/compiler/basicTypes/Module.hs
index 1cf0cbfa97..a20de2d0b3 100644
--- a/compiler/basicTypes/Module.hs
+++ b/compiler/basicTypes/Module.hs
@@ -326,11 +326,13 @@ stablePackageKeyCmp p1 p2 = packageKeyFS p1 `compare` packageKeyFS p2
 
 instance Outputable PackageKey where
    ppr pk = getPprStyle $ \sty -> sdocWithDynFlags $ \dflags ->
-    text (packageKeyPackageIdString dflags pk)
-    -- Don't bother qualifying if it's wired in!
-       <> (if qualPackage sty pk && not (pk `elem` wiredInPackageKeys)
-            then char '@' <> ftext (packageKeyFS pk)
-            else empty)
+    case packageKeyPackageIdString dflags pk of
+      Nothing -> ftext (packageKeyFS pk)
+      Just pkg -> text pkg
+           -- Don't bother qualifying if it's wired in!
+           <> (if qualPackage sty pk && not (pk `elem` wiredInPackageKeys)
+                then char '@' <> ftext (packageKeyFS pk)
+                else empty)
 
 instance Binary PackageKey where
   put_ bh pid = put_ bh (packageKeyFS pid)
diff --git a/compiler/main/Packages.hs b/compiler/main/Packages.hs
index 4f8afb5e91..70476a16bd 100644
--- a/compiler/main/Packages.hs
+++ b/compiler/main/Packages.hs
@@ -1354,12 +1354,10 @@ missingDependencyMsg (Just parent)
 
 -- -----------------------------------------------------------------------------
 
-packageKeyPackageIdString :: DynFlags -> PackageKey -> String
+packageKeyPackageIdString :: DynFlags -> PackageKey -> Maybe String
 packageKeyPackageIdString dflags pkg_key
-    | pkg_key == mainPackageKey = "main"
-    | otherwise = maybe "(unknown)"
-                      sourcePackageIdString
-                      (lookupPackage dflags pkg_key)
+    | pkg_key == mainPackageKey = Just "main"
+    | otherwise = fmap sourcePackageIdString (lookupPackage dflags pkg_key)
 
 -- | Will the 'Name' come from a dynamically linked library?
 isDllName :: DynFlags -> PackageKey -> Module -> Name -> Bool
diff --git a/compiler/main/Packages.hs-boot b/compiler/main/Packages.hs-boot
index 2f898f19d3..f2343b66c9 100644
--- a/compiler/main/Packages.hs-boot
+++ b/compiler/main/Packages.hs-boot
@@ -3,4 +3,4 @@ module Packages where
 import {-# SOURCE #-} Module (PackageKey)
 import {-# SOURCE #-} DynFlags (DynFlags)
 data PackageState
-packageKeyPackageIdString :: DynFlags -> PackageKey -> String
+packageKeyPackageIdString :: DynFlags -> PackageKey -> Maybe String