diff --git a/win32port/zlib/crc32.c b/win32port/zlib/crc32.c
index bf04a559..66ad1858 100644
--- a/win32port/zlib/crc32.c
+++ b/win32port/zlib/crc32.c
@@ -295,7 +295,7 @@ local unsigned long crc32_little(crc, buf, len)
 }
 
 /* ========================================================================= */
-#define DOBIG4 c ^= *++buf4; \
+#define DOBIG4 c ^= *buf4++; \
         c = crc_table[4][c & 0xff] ^ crc_table[5][(c >> 8) & 0xff] ^ \
             crc_table[6][(c >> 16) & 0xff] ^ crc_table[7][c >> 24]
 #define DOBIG32 DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4; DOBIG4
@@ -317,7 +317,6 @@ local unsigned long crc32_big(crc, buf, len)
     }
 
     buf4 = (const u4 FAR *)(const void FAR *)buf;
-    buf4--;
     while (len >= 32) {
         DOBIG32;
         len -= 32;
@@ -326,7 +325,6 @@ local unsigned long crc32_big(crc, buf, len)
         DOBIG4;
         len -= 4;
     }
-    buf4++;
     buf = (const unsigned char FAR *)buf4;
 
     if (len) do {