diff --git a/ext/psych/yaml/yaml_private.h b/ext/psych/yaml/yaml_private.h
index abb7b9bbd3..21fc5e4326 100644
--- a/ext/psych/yaml/yaml_private.h
+++ b/ext/psych/yaml/yaml_private.h
@@ -1,3 +1,6 @@
+#ifdef RUBY_EXTCONF_H
+#include RUBY_EXTCONF_H
+#endif
 
 #if HAVE_CONFIG_H
 #include <config.h>