diff --git a/zlib/inflate.c b/zlib/inflate.c
index 1afe007aa..1836d265f 100644
--- a/zlib/inflate.c
+++ b/zlib/inflate.c
@@ -229,7 +229,7 @@ int ZEXPORT inflatePrime(z_streamp strm, int bits, int value)
     }
     if (bits > 16 || state->bits + bits > 32) return Z_STREAM_ERROR;
     value &= (1L << bits) - 1;
-    state->hold += value << state->bits;
+    state->hold += (unsigned long)value << state->bits;
     state->bits += bits;
     return Z_OK;
 }