diff --git a/src/dropin.h b/src/dropin.h
index 61143eb8..5279de79 100644
--- a/src/dropin.h
+++ b/src/dropin.h
@@ -58,7 +58,7 @@ extern int usleep(long long usec);
 #define timersub(a, b, r) do {\
 	(r)->tv_sec = (a)->tv_sec - (b)->tv_sec;\
 	(r)->tv_usec = (a)->tv_usec - (b)->tv_usec;\
-	if((r)->tv_usec < 1000000)\
+	if((r)->tv_usec < 0)\
 		(r)->tv_sec--, (r)->tv_usec += 1000000;\
 } while (0)
 #endif