diff --git a/src/if_python3.c b/src/if_python3.c
index 1de8fe8..188e9c3 100644
--- a/src/if_python3.c
+++ b/src/if_python3.c
@@ -45,6 +45,9 @@
 # undef F_BLANK
 #endif
 
+#ifdef HAVE_DUP
+# undef HAVE_DUP
+#endif
 #ifdef HAVE_STRFTIME
 # undef HAVE_STRFTIME
 #endif