diff --git a/mm/circbuf/circbuf.c b/mm/circbuf/circbuf.c
index c4d16e90309..0912e524e71 100644
--- a/mm/circbuf/circbuf.c
+++ b/mm/circbuf/circbuf.c
@@ -103,7 +103,7 @@ int circbuf_init(FAR struct circbuf_s *circ, FAR void *base, size_t bytes)
 int circbuf_resize(FAR struct circbuf_s *circ, size_t bytes)
 {
   FAR void *tmp = NULL;
-  size_t len;
+  size_t len = 0;
 
   DEBUGASSERT(circ);
   DEBUGASSERT(!circ->external);