diff --git a/src/misc/haiku/SDL_sysurl.cc b/src/misc/haiku/SDL_sysurl.cc
index 150028dd5..72039a8e5 100644
--- a/src/misc/haiku/SDL_sysurl.cc
+++ b/src/misc/haiku/SDL_sysurl.cc
@@ -23,6 +23,8 @@
 #include "SDL_error.h"
 #include <Url.h>
 
+extern "C" { int SDL_SYS_OpenURL(const char *url); }
+
 int
 SDL_SYS_OpenURL(const char *url)
 {