diff --git a/System/Directory/ModTime.hs b/System/Directory/ModTime.hs
index 563a366..0e38eae 100644
--- a/System/Directory/ModTime.hs
+++ b/System/Directory/ModTime.hs
@@ -42,7 +42,7 @@ instance Binary ModTime where
 #else
 
 newtype ModTime = ModTime ClockTime
-    deriving (Eq, Ord, NFData)
+    deriving (Eq, Ord)
 getCurrentModTime = ModTime <$> getClockTime
 
 instance Binary ModTime where
@@ -51,6 +51,10 @@ instance Binary ModTime where
     get =
         ModTime <$> (TOD <$> get <*> get)
 
+instance NFData ModTime where
+    rnf (ModTime (TOD s ps)) =
+        s `seq` ps `seq` (ModTime $! TOD s ps) `seq` ()
+
 #endif
 
 getCurrentModTime :: IO ModTime