diff --git a/drd/drd_main.c b/drd/drd_main.c
index 3b92a9ab8..63e1bb065 100644
--- a/drd/drd_main.c
+++ b/drd/drd_main.c
@@ -326,6 +326,9 @@ void drd_stop_using_mem(const Addr a1, const SizeT len,
 {
    const Addr a2 = a1 + len;
 
+   if (len == 0)
+      return;
+
    tl_assert(a1 < a2);
 
    if (UNLIKELY(DRD_(any_address_is_traced)()))