diff --git a/libavcodec/wmaprodec.c b/libavcodec/wmaprodec.c
index 419523590b..aa068264bd 100644
--- a/libavcodec/wmaprodec.c
+++ b/libavcodec/wmaprodec.c
@@ -1130,7 +1130,7 @@ static int decode_subframe(WMAProDecodeCtx *s)
         int num_fill_bits;
         if (!(num_fill_bits = get_bits(&s->gb, 2))) {
             int len = get_bits(&s->gb, 4);
-            num_fill_bits = get_bits(&s->gb, len) + 1;
+            num_fill_bits = (len ? get_bits(&s->gb, len) : 0) + 1;
         }
 
         if (num_fill_bits >= 0) {