diff --git a/libavcodec/truespeech.c b/libavcodec/truespeech.c
index 799cef0945..d7c2d535e2 100644
--- a/libavcodec/truespeech.c
+++ b/libavcodec/truespeech.c
@@ -254,7 +254,7 @@ static void truespeech_synth(TSContext *dec, int16_t *out, int quart)
     for(i = 0; i < 60; i++){
         int sum = 0;
         for(k = 0; k < 8; k++)
-            sum += ptr0[k] * ptr1[k];
+            sum += ptr0[k] * (unsigned)ptr1[k];
         sum = out[i] + ((sum + 0x800) >> 12);
         out[i] = av_clip(sum, -0x7FFE, 0x7FFE);
         for(k = 7; k > 0; k--)