diff --git a/README.md b/README.md
index 7a94089..1c8a3f8 100644
--- a/README.md
+++ b/README.md
@@ -372,7 +372,7 @@ $
 
 ### [pre](/sh/pre)
 
-(bash/zsh) dumps all the #defines that `$CC $CFLAGS $LDFLAGS` would result in.
+(bash/zsh) dumps all the #defines that `$CC $CPPFLAGS $CFLAGS $LDFLAGS` would result in.
 
 ```
 $ pre | shuf | head -10
diff --git a/sh/pre b/sh/pre
index 85da5d5..16c4079 100755
--- a/sh/pre
+++ b/sh/pre
@@ -1,6 +1,6 @@
 #!/usr/bin/env bash
 if [ -n "${ZSH_VERSION:-}" ]; then
-    $CC -dM -E - $=CFLAGS $=LDFLAGS < /dev/null
+    $CC -dM -E - $=CPPFLAGS $=CFLAGS $=LDFLAGS < /dev/null
 else
-    $CC -dM -E - $CFLAGS $LDFLAGS < /dev/null
+    $CC -dM -E - $CPPFLAGS $CFLAGS $LDFLAGS < /dev/null
 fi