diff --git a/ext/interbase/config.m4 b/ext/interbase/config.m4
index ceb84932d11..2231d94753a 100644
--- a/ext/interbase/config.m4
+++ b/ext/interbase/config.m4
@@ -21,7 +21,7 @@ if test "$PHP_INTERBASE" != "no"; then
   ], [
     AC_MSG_ERROR([libgds not found! Check config.log for more information.])
   ], [
-    -L$IBASE_LIBDIR -lgds
+    -L$IBASE_LIBDIR -lgds -lcrypt
   ])
 
   PHP_ADD_INCLUDE($IBASE_INCDIR)