diff --git a/sys/lib/libz/crc32.c b/sys/lib/libz/crc32.c
index a1129e87521a..df94f8e73d24 100644
--- a/sys/lib/libz/crc32.c
+++ b/sys/lib/libz/crc32.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: crc32.c,v 1.14 2022/05/08 14:05:29 tb Exp $ */
+/*	$OpenBSD: crc32.c,v 1.15 2022/05/08 14:07:54 tb Exp $ */
 /* crc32.c -- compute the CRC-32 of a data stream
  * Copyright (C) 1995-2022 Mark Adler
  * For conditions of distribution and use, see copyright notice in zlib.h
@@ -629,7 +629,7 @@ unsigned long ZEXPORT crc32_z(crc, buf, len)
 #endif /* DYNAMIC_CRC_TABLE */
 
     /* Pre-condition the CRC */
-    crc ^= 0xffffffff;
+    crc = (~crc) & 0xffffffff;
 
     /* Compute the CRC up to a word boundary. */
     while (len && ((z_size_t)buf & 7) != 0) {
@@ -748,7 +748,7 @@ unsigned long ZEXPORT crc32_z(crc, buf, len)
 #endif /* DYNAMIC_CRC_TABLE */
 
     /* Pre-condition the CRC */
-    crc ^= 0xffffffff;
+    crc = (~crc) & 0xffffffff;
 
 #ifdef W
 
@@ -1076,7 +1076,7 @@ uLong ZEXPORT crc32_combine64(crc1, crc2, len2)
 #ifdef DYNAMIC_CRC_TABLE
     once(&made, make_crc_table);
 #endif /* DYNAMIC_CRC_TABLE */
-    return multmodp(x2nmodp(len2, 3), crc1) ^ crc2;
+    return multmodp(x2nmodp(len2, 3), crc1) ^ (crc2 & 0xffffffff);
 }
 
 /* ========================================================================= */
@@ -1111,5 +1111,5 @@ uLong crc32_combine_op(crc1, crc2, op)
     uLong crc2;
     uLong op;
 {
-    return multmodp(op, crc1) ^ crc2;
+    return multmodp(op, crc1) ^ (crc2 & 0xffffffff);
 }