diff --git a/lib/replace/replace.h b/lib/replace/replace.h
index adcb22f8c19..a6a2b40777f 100644
--- a/lib/replace/replace.h
+++ b/lib/replace/replace.h
@@ -41,7 +41,7 @@
  * As it's also needed when Python.h is the first header we
  * require a global -D__STDC_WANT_LIB_EXT1__=1
  */
-#ifndef __STDC_WANT_LIB_EXT1__
+#if __STDC_WANT_LIB_EXT1__ != 1
 #error -D__STDC_WANT_LIB_EXT1__=1 required
 #endif