diff --git a/libavcodec/i386/dsputil_mmx.c b/libavcodec/i386/dsputil_mmx.c
index b937ef5565..a05eb9e658 100644
--- a/libavcodec/i386/dsputil_mmx.c
+++ b/libavcodec/i386/dsputil_mmx.c
@@ -1441,10 +1441,12 @@ void dsputil_init_mmx(DSPContext* c, AVCodecContext *avctx)
 {
     mm_flags = mm_support();
 
-    if (avctx->dsp_mask && FF_MM_FORCE)
-	mm_flags |= (avctx->dsp_mask & 0xffff);
-    else
-        mm_flags &= (avctx->dsp_mask & 0xffff);
+    if (avctx->dsp_mask) {
+	if (avctx->dsp_mask & FF_MM_FORCE)
+	    mm_flags |= (avctx->dsp_mask & 0xffff);
+	else
+	    mm_flags &= ~(avctx->dsp_mask & 0xffff);
+    }
 
 #if 0
     fprintf(stderr, "libavcodec: CPU flags:");