diff --git a/src/if_python3.c b/src/if_python3.c
index 7d69b0c..84302bd 100644
--- a/src/if_python3.c
+++ b/src/if_python3.c
@@ -51,6 +51,15 @@
 # undef F_BLANK
 #endif
 
+#ifdef HAVE_STRFTIME
+# undef HAVE_STRFTIME
+#endif
+#ifdef HAVE_STRING_H
+# undef HAVE_STRING_H
+#endif
+#ifdef HAVE_PUTENV
+# undef HAVE_PUTENV
+#endif
 #ifdef HAVE_STDARG_H
 # undef HAVE_STDARG_H   /* Python's config.h defines it as well. */
 #endif