diff --git a/os/backtrace.c b/os/backtrace.c
index 9e3e38edf7..619bf145ec 100644
--- a/os/backtrace.c
+++ b/os/backtrace.c
@@ -78,6 +78,7 @@ xorg_backtrace(void)
             break;
         }
 
+        off = 0;
         ret = unw_get_proc_name(&cursor, procname, 256, &off);
         if (ret && ret != -UNW_ENOMEM) {
             if (ret != -UNW_EUNSPEC)