diff --git a/include/zlib.h b/include/zlib.h
index 3f6c2b27b..68439b290 100644
--- a/include/zlib.h
+++ b/include/zlib.h
@@ -114,7 +114,8 @@ int __fastcall__ uncompress (unsigned char* dest, unsigned* destLen,
 */
 
 
-unsigned long __fastcall__ adler32 (unsigned long adler, const char* buf,
+unsigned long __fastcall__ adler32 (unsigned long adler,
+                                    const unsigned char* buf,
                                     unsigned len);
 
 /*
@@ -140,7 +141,8 @@ unsigned long __fastcall__ adler32 (unsigned long adler, const char* buf,
 */
 
 
-unsigned long __fastcall__ crc32 (unsigned long crc, const char* buf,
+unsigned long __fastcall__ crc32 (unsigned long crc,
+                                  const unsigned char* buf,
                                   unsigned len);
 /*
    Original zlib description:
diff --git a/libsrc/zlib/adler32.s b/libsrc/zlib/adler32.s
index 8aa641a13..1bb5588db 100644
--- a/libsrc/zlib/adler32.s
+++ b/libsrc/zlib/adler32.s
@@ -2,7 +2,8 @@
 ; 2001-11-18, Piotr Fusik
 ; 2018-05-20, Christian Kruger
 ;
-; unsigned long __fastcall__ adler32 (unsigned long adler, unsigned char* buf,
+; unsigned long __fastcall__ adler32 (unsigned long adler,
+;                                     const unsigned char* buf,
 ;                                     unsigned len);
 ;
 
diff --git a/libsrc/zlib/crc32.s b/libsrc/zlib/crc32.s
index f019736ad..41b5fe9db 100644
--- a/libsrc/zlib/crc32.s
+++ b/libsrc/zlib/crc32.s
@@ -2,7 +2,8 @@
 ; 2001-11-14, Piotr Fusik
 ; 2018-05-20, Christian Kruger
 ;
-; unsigned long __fastcall__ crc32 (unsigned long crc, unsigned char* buf,
+; unsigned long __fastcall__ crc32 (unsigned long crc,
+;                                   const unsigned char* buf,
 ;                                   unsigned len);
 ;