diff --git a/gc.c b/gc.c
index ea4d3b0078..2d25d51fb5 100644
--- a/gc.c
+++ b/gc.c
@@ -1002,6 +1002,8 @@ free_unused_heaps(void)
     }
 }
 
+void rb_gc_abort_threads(void);
+
 static void
 gc_sweep(void)
 {