diff --git a/libavutil/softfloat.h b/libavutil/softfloat.h
index fa91d1e1cb..fed3e77f87 100644
--- a/libavutil/softfloat.h
+++ b/libavutil/softfloat.h
@@ -235,12 +235,12 @@ static av_unused void av_sincos_sf(int a, int *s, int *c)
     int st, ct;
 
     idx = a >> 26;
-    sign = (idx << 27) >> 31;
+    sign = (int32_t)((unsigned)idx << 27) >> 31;
     cv = av_costbl_1_sf[idx & 0xf];
     cv = (cv ^ sign) - sign;
 
     idx -= 8;
-    sign = (idx << 27) >> 31;
+    sign = (int32_t)((unsigned)idx << 27) >> 31;
     sv = av_costbl_1_sf[idx & 0xf];
     sv = (sv ^ sign) - sign;