--- a/tools/checkasm.c
+++ b/tools/checkasm.c
@@ -846,7 +846,7 @@ static int check_mc( int cpu_ref, int cpu_new )
             call_a( mc_a.mc_chroma, dst2, dst2+8, 16, src, 64, dx, dy, w, h ); \
             /* mc_chroma width=2 may write garbage to the right of dst. ignore that. */\
             for( int j = 0; j < h; j++ ) \
-                for( int i = w; i < 8; i++ ) \
+                for( int i = w; i < 4; i++ ) \
                 { \
                     dst2[i+j*16+8] = dst1[i+j*16+8]; \
                     dst2[i+j*16] = dst1[i+j*16]; \