diff --git a/src/backend/port/bsdi_2_1/port-protos.h b/src/backend/port/bsdi_2_1/port-protos.h
index 24a61155ee..5aab562a4b 100644
--- a/src/backend/port/bsdi_2_1/port-protos.h
+++ b/src/backend/port/bsdi_2_1/port-protos.h
@@ -13,6 +13,7 @@
 #ifndef PORT_PROTOS_H
 #define PORT_PROTOS_H
 
+#include <dlfcn.h>
 #include "fmgr.h"			/* for func_ptr */
 #include "utils/dynamic_loader.h"