diff --git a/osdep.h b/osdep.h
index 0acffa44a1..c8ab667b4d 100644
--- a/osdep.h
+++ b/osdep.h
@@ -56,6 +56,8 @@ void *get_mmap_addr(unsigned long size);
 int qemu_create_pidfile(const char *filename);
 
 #ifdef _WIN32
+int ffs(int i);
+
 typedef struct {
     long tv_sec;
     long tv_usec;