diff --git a/System/Process/Internals.hs b/System/Process/Internals.hs
index c4d5be3b..af420093 100644
--- a/System/Process/Internals.hs
+++ b/System/Process/Internals.hs
@@ -50,7 +50,7 @@ import System.Posix.Internals (FD)
 
 import System.Process.Common
 
-#if WINDOWS
+#ifdef WINDOWS
 import System.Process.Windows
 #else
 import System.Process.Posix