diff --git a/libavcodec/x86/dsputilenc_mmx.c b/libavcodec/x86/dsputilenc_mmx.c
index 1717a01..c1a648b 100644
--- a/libavcodec/x86/dsputilenc_mmx.c
+++ b/libavcodec/x86/dsputilenc_mmx.c
@@ -882,6 +882,7 @@
 
 static void diff_bytes_mmx(uint8_t *dst, uint8_t *src1, uint8_t *src2, int w){
     x86_reg i=0;
+    if(w>=16)
     __asm__ volatile(
         "1:                             \n\t"
         "movq  (%2, %0), %%mm0          \n\t"