diff --git a/Source/3rd Party/zlib/trees.c b/Source/3rd Party/zlib/trees.c
index 56e9bb1c1..747ca2944 100644
--- a/Source/3rd Party/zlib/trees.c	
+++ b/Source/3rd Party/zlib/trees.c	
@@ -204,7 +204,7 @@ local void send_bits(s, value, length)
      * unused bits in value.
      */
     if (s->bi_valid > (int)Buf_size - length) {
-        s->bi_buf |= (ush)value << s->bi_valid;
+        s->bi_buf |= (value << s->bi_valid) & 0xFFFF;
         put_short(s, s->bi_buf);
         s->bi_buf = (ush)value >> (Buf_size - s->bi_valid);
         s->bi_valid += length - Buf_size;