diff --git a/libavcodec/truemotion2.c b/libavcodec/truemotion2.c
index c583ff4032..1aa7a4b870 100644
--- a/libavcodec/truemotion2.c
+++ b/libavcodec/truemotion2.c
@@ -591,7 +591,8 @@ static inline void tm2_null_res_block(TM2Context *ctx, AVFrame *pic, int bx, int
 {
     int i;
     int ct;
-    int left, right, diff;
+    unsigned left, right;
+    int diff;
     int deltas[16];
     TM2_INIT_POINTERS();