diff --git a/contrib/infback9/infback9.c b/contrib/infback9/infback9.c
index 742a39214..4ac4c3d6d 100644
--- a/contrib/infback9/infback9.c
+++ b/contrib/infback9/infback9.c
@@ -293,7 +293,7 @@ int ZEXPORT inflateBack9(z_stream FAR *strm, in_func in, void FAR *in_desc,
                 mode = TABLE;
                 break;
             case 3:
-                strm->msg = (char *)"invalid block type";
+                strm->msg = (z_const char *)"invalid block type";
                 mode = BAD;
             }
             DROPBITS(2);
@@ -304,7 +304,7 @@ int ZEXPORT inflateBack9(z_stream FAR *strm, in_func in, void FAR *in_desc,
             BYTEBITS();                         /* go to byte boundary */
             NEEDBITS(32);
             if ((hold & 0xffff) != ((hold >> 16) ^ 0xffff)) {
-                strm->msg = (char *)"invalid stored block lengths";
+                strm->msg = (z_const char *)"invalid stored block lengths";
                 mode = BAD;
                 break;
             }
@@ -341,7 +341,7 @@ int ZEXPORT inflateBack9(z_stream FAR *strm, in_func in, void FAR *in_desc,
             state->ncode = BITS(4) + 4;
             DROPBITS(4);
             if (state->nlen > 286) {
-                strm->msg = (char *)"too many length symbols";
+                strm->msg = (z_const char *)"too many length symbols";
                 mode = BAD;
                 break;
             }
@@ -362,7 +362,7 @@ int ZEXPORT inflateBack9(z_stream FAR *strm, in_func in, void FAR *in_desc,
             ret = inflate_table9(CODES, state->lens, 19, &(state->next),
                                 &(lenbits), state->work);
             if (ret) {
-                strm->msg = (char *)"invalid code lengths set";
+                strm->msg = (z_const char *)"invalid code lengths set";
                 mode = BAD;
                 break;
             }
@@ -386,7 +386,7 @@ int ZEXPORT inflateBack9(z_stream FAR *strm, in_func in, void FAR *in_desc,
                         NEEDBITS(here.bits + 2);
                         DROPBITS(here.bits);
                         if (state->have == 0) {
-                            strm->msg = (char *)"invalid bit length repeat";
+                            strm->msg = (z_const char *)"invalid bit length repeat";
                             mode = BAD;
                             break;
                         }
@@ -409,7 +409,7 @@ int ZEXPORT inflateBack9(z_stream FAR *strm, in_func in, void FAR *in_desc,
                         DROPBITS(7);
                     }
                     if (state->have + copy > state->nlen + state->ndist) {
-                        strm->msg = (char *)"invalid bit length repeat";
+                        strm->msg = (z_const char *)"invalid bit length repeat";
                         mode = BAD;
                         break;
                     }
@@ -423,7 +423,7 @@ int ZEXPORT inflateBack9(z_stream FAR *strm, in_func in, void FAR *in_desc,
 
             /* check for end-of-block code (better have one) */
             if (state->lens[256] == 0) {
-                strm->msg = (char *)"invalid code -- missing end-of-block";
+                strm->msg = (z_const char *)"invalid code -- missing end-of-block";
                 mode = BAD;
                 break;
             }
@@ -437,7 +437,7 @@ int ZEXPORT inflateBack9(z_stream FAR *strm, in_func in, void FAR *in_desc,
             ret = inflate_table9(LENS, state->lens, state->nlen,
                             &(state->next), &(lenbits), state->work);
             if (ret) {
-                strm->msg = (char *)"invalid literal/lengths set";
+                strm->msg = (z_const char *)"invalid literal/lengths set";
                 mode = BAD;
                 break;
             }
@@ -447,7 +447,7 @@ int ZEXPORT inflateBack9(z_stream FAR *strm, in_func in, void FAR *in_desc,
                             state->ndist, &(state->next), &(distbits),
                             state->work);
             if (ret) {
-                strm->msg = (char *)"invalid distances set";
+                strm->msg = (z_const char *)"invalid distances set";
                 mode = BAD;
                 break;
             }
@@ -495,7 +495,7 @@ int ZEXPORT inflateBack9(z_stream FAR *strm, in_func in, void FAR *in_desc,
 
             /* invalid code */
             if (here.op & 64) {
-                strm->msg = (char *)"invalid literal/length code";
+                strm->msg = (z_const char *)"invalid literal/length code";
                 mode = BAD;
                 break;
             }
@@ -527,7 +527,7 @@ int ZEXPORT inflateBack9(z_stream FAR *strm, in_func in, void FAR *in_desc,
             }
             DROPBITS(here.bits);
             if (here.op & 64) {
-                strm->msg = (char *)"invalid distance code";
+                strm->msg = (z_const char *)"invalid distance code";
                 mode = BAD;
                 break;
             }
@@ -541,7 +541,7 @@ int ZEXPORT inflateBack9(z_stream FAR *strm, in_func in, void FAR *in_desc,
                 DROPBITS(extra);
             }
             if (offset > WSIZE - (wrap ? 0: left)) {
-                strm->msg = (char *)"invalid distance too far back";
+                strm->msg = (z_const char *)"invalid distance too far back";
                 mode = BAD;
                 break;
             }
diff --git a/examples/gun.c b/examples/gun.c
index bea5497e5..dbd181c07 100644
--- a/examples/gun.c
+++ b/examples/gun.c
@@ -227,12 +227,12 @@ local int lunpipe(unsigned have, z_const unsigned char *next, struct ind *indp,
     if (last == -1)
         return Z_BUF_ERROR;
     if (flags & 0x60) {
-        strm->msg = (char *)"unknown lzw flags set";
+        strm->msg = (z_const char *)"unknown lzw flags set";
         return Z_DATA_ERROR;
     }
     max = flags & 0x1f;
     if (max < 9 || max > 16) {
-        strm->msg = (char *)"lzw bits out of range";
+        strm->msg = (z_const char *)"lzw bits out of range";
         return Z_DATA_ERROR;
     }
     if (max == 9)                           /* 9 doesn't really mean 9 */
@@ -252,7 +252,7 @@ local int lunpipe(unsigned have, z_const unsigned char *next, struct ind *indp,
     if (NEXT() == -1)                       /* missing a bit */
         return Z_BUF_ERROR;
     if (last & 1) {                         /* code must be < 256 */
-        strm->msg = (char *)"invalid lzw code";
+        strm->msg = (z_const char *)"invalid lzw code";
         return Z_DATA_ERROR;
     }
     rem = (unsigned)last >> 1;              /* remaining 7 bits */
@@ -319,7 +319,7 @@ local int lunpipe(unsigned have, z_const unsigned char *next, struct ind *indp,
                to detect random or corrupted input after a compress header.
                In any case, the prev > end check must be retained. */
             if (code != end + 1 || prev > end) {
-                strm->msg = (char *)"invalid lzw code";
+                strm->msg = (z_const char *)"invalid lzw code";
                 return Z_DATA_ERROR;
             }
             match[stack++] = (unsigned char)final;
@@ -404,7 +404,7 @@ local int gunpipe(z_stream *strm, int infile, int outfile)
             break;                          /* empty gzip stream is ok */
         }
         if (last != 31 || (NEXT() != 139 && last != 157)) {
-            strm->msg = (char *)"incorrect header check";
+            strm->msg = (z_const char *)"incorrect header check";
             ret = first ? Z_DATA_ERROR : Z_ERRNO;
             break;                          /* not a gzip or compress header */
         }
@@ -420,7 +420,7 @@ local int gunpipe(z_stream *strm, int infile, int outfile)
         ret = Z_BUF_ERROR;
         if (NEXT() != 8) {                  /* only deflate method allowed */
             if (last == -1) break;
-            strm->msg = (char *)"unknown compression method";
+            strm->msg = (z_const char *)"unknown compression method";
             ret = Z_DATA_ERROR;
             break;
         }
@@ -433,7 +433,7 @@ local int gunpipe(z_stream *strm, int infile, int outfile)
         NEXT();
         if (last == -1) break;
         if (flags & 0xe0) {
-            strm->msg = (char *)"unknown header flags set";
+            strm->msg = (z_const char *)"unknown header flags set";
             ret = Z_DATA_ERROR;
             break;
         }
@@ -486,7 +486,7 @@ local int gunpipe(z_stream *strm, int infile, int outfile)
             NEXT() != (int)((outd.crc >> 24) & 0xff)) {
             /* crc error */
             if (last != -1) {
-                strm->msg = (char *)"incorrect data check";
+                strm->msg = (z_const char *)"incorrect data check";
                 ret = Z_DATA_ERROR;
             }
             break;
@@ -497,7 +497,7 @@ local int gunpipe(z_stream *strm, int infile, int outfile)
             NEXT() != (int)((outd.total >> 24) & 0xff)) {
             /* length error */
             if (last != -1) {
-                strm->msg = (char *)"incorrect length check";
+                strm->msg = (z_const char *)"incorrect length check";
                 ret = Z_DATA_ERROR;
             }
             break;
diff --git a/infback.c b/infback.c
index e7b25b307..fd02e7090 100644
--- a/infback.c
+++ b/infback.c
@@ -304,7 +304,7 @@ int ZEXPORT inflateBack(z_streamp strm, in_func in, void FAR *in_desc,
                 state->mode = TABLE;
                 break;
             case 3:
-                strm->msg = (char *)"invalid block type";
+                strm->msg = (z_const char *)"invalid block type";
                 state->mode = BAD;
             }
             DROPBITS(2);
@@ -315,7 +315,7 @@ int ZEXPORT inflateBack(z_streamp strm, in_func in, void FAR *in_desc,
             BYTEBITS();                         /* go to byte boundary */
             NEEDBITS(32);
             if ((hold & 0xffff) != ((hold >> 16) ^ 0xffff)) {
-                strm->msg = (char *)"invalid stored block lengths";
+                strm->msg = (z_const char *)"invalid stored block lengths";
                 state->mode = BAD;
                 break;
             }
@@ -353,7 +353,7 @@ int ZEXPORT inflateBack(z_streamp strm, in_func in, void FAR *in_desc,
             DROPBITS(4);
 #ifndef PKZIP_BUG_WORKAROUND
             if (state->nlen > 286 || state->ndist > 30) {
-                strm->msg = (char *)"too many length or distance symbols";
+                strm->msg = (z_const char *)"too many length or distance symbols";
                 state->mode = BAD;
                 break;
             }
@@ -375,7 +375,7 @@ int ZEXPORT inflateBack(z_streamp strm, in_func in, void FAR *in_desc,
             ret = inflate_table(CODES, state->lens, 19, &(state->next),
                                 &(state->lenbits), state->work);
             if (ret) {
-                strm->msg = (char *)"invalid code lengths set";
+                strm->msg = (z_const char *)"invalid code lengths set";
                 state->mode = BAD;
                 break;
             }
@@ -398,7 +398,7 @@ int ZEXPORT inflateBack(z_streamp strm, in_func in, void FAR *in_desc,
                         NEEDBITS(here.bits + 2);
                         DROPBITS(here.bits);
                         if (state->have == 0) {
-                            strm->msg = (char *)"invalid bit length repeat";
+                            strm->msg = (z_const char *)"invalid bit length repeat";
                             state->mode = BAD;
                             break;
                         }
@@ -421,7 +421,7 @@ int ZEXPORT inflateBack(z_streamp strm, in_func in, void FAR *in_desc,
                         DROPBITS(7);
                     }
                     if (state->have + copy > state->nlen + state->ndist) {
-                        strm->msg = (char *)"invalid bit length repeat";
+                        strm->msg = (z_const char *)"invalid bit length repeat";
                         state->mode = BAD;
                         break;
                     }
@@ -435,7 +435,7 @@ int ZEXPORT inflateBack(z_streamp strm, in_func in, void FAR *in_desc,
 
             /* check for end-of-block code (better have one) */
             if (state->lens[256] == 0) {
-                strm->msg = (char *)"invalid code -- missing end-of-block";
+                strm->msg = (z_const char *)"invalid code -- missing end-of-block";
                 state->mode = BAD;
                 break;
             }
@@ -449,7 +449,7 @@ int ZEXPORT inflateBack(z_streamp strm, in_func in, void FAR *in_desc,
             ret = inflate_table(LENS, state->lens, state->nlen, &(state->next),
                                 &(state->lenbits), state->work);
             if (ret) {
-                strm->msg = (char *)"invalid literal/lengths set";
+                strm->msg = (z_const char *)"invalid literal/lengths set";
                 state->mode = BAD;
                 break;
             }
@@ -458,7 +458,7 @@ int ZEXPORT inflateBack(z_streamp strm, in_func in, void FAR *in_desc,
             ret = inflate_table(DISTS, state->lens + state->nlen, state->ndist,
                             &(state->next), &(state->distbits), state->work);
             if (ret) {
-                strm->msg = (char *)"invalid distances set";
+                strm->msg = (z_const char *)"invalid distances set";
                 state->mode = BAD;
                 break;
             }
@@ -517,7 +517,7 @@ int ZEXPORT inflateBack(z_streamp strm, in_func in, void FAR *in_desc,
 
             /* invalid code */
             if (here.op & 64) {
-                strm->msg = (char *)"invalid literal/length code";
+                strm->msg = (z_const char *)"invalid literal/length code";
                 state->mode = BAD;
                 break;
             }
@@ -549,7 +549,7 @@ int ZEXPORT inflateBack(z_streamp strm, in_func in, void FAR *in_desc,
             }
             DROPBITS(here.bits);
             if (here.op & 64) {
-                strm->msg = (char *)"invalid distance code";
+                strm->msg = (z_const char *)"invalid distance code";
                 state->mode = BAD;
                 break;
             }
@@ -564,7 +564,7 @@ int ZEXPORT inflateBack(z_streamp strm, in_func in, void FAR *in_desc,
             }
             if (state->offset > state->wsize - (state->whave < state->wsize ?
                                                 left : 0)) {
-                strm->msg = (char *)"invalid distance too far back";
+                strm->msg = (z_const char *)"invalid distance too far back";
                 state->mode = BAD;
                 break;
             }
diff --git a/inffast.c b/inffast.c
index 9354676e7..f7b550b8b 100644
--- a/inffast.c
+++ b/inffast.c
@@ -155,7 +155,7 @@ void ZLIB_INTERNAL inflate_fast(z_streamp strm, unsigned start) {
                 dist += (unsigned)hold & ((1U << op) - 1);
 #ifdef INFLATE_STRICT
                 if (dist > dmax) {
-                    strm->msg = (char *)"invalid distance too far back";
+                    strm->msg = (z_const char *)"invalid distance too far back";
                     state->mode = BAD;
                     break;
                 }
@@ -169,7 +169,7 @@ void ZLIB_INTERNAL inflate_fast(z_streamp strm, unsigned start) {
                     if (op > whave) {
                         if (state->sane) {
                             strm->msg =
-                                (char *)"invalid distance too far back";
+                                (z_const char *)"invalid distance too far back";
                             state->mode = BAD;
                             break;
                         }
@@ -265,7 +265,7 @@ void ZLIB_INTERNAL inflate_fast(z_streamp strm, unsigned start) {
                 goto dodist;
             }
             else {
-                strm->msg = (char *)"invalid distance code";
+                strm->msg = (z_const char *)"invalid distance code";
                 state->mode = BAD;
                 break;
             }
@@ -280,7 +280,7 @@ void ZLIB_INTERNAL inflate_fast(z_streamp strm, unsigned start) {
             break;
         }
         else {
-            strm->msg = (char *)"invalid literal/length code";
+            strm->msg = (z_const char *)"invalid literal/length code";
             state->mode = BAD;
             break;
         }
diff --git a/inflate.c b/inflate.c
index 94ecff015..e2fa6bb1a 100644
--- a/inflate.c
+++ b/inflate.c
@@ -642,12 +642,12 @@ int ZEXPORT inflate(z_streamp strm, int flush) {
             if (
 #endif
                 ((BITS(8) << 8) + (hold >> 8)) % 31) {
-                strm->msg = (char *)"incorrect header check";
+                strm->msg = (z_const char *)"incorrect header check";
                 state->mode = BAD;
                 break;
             }
             if (BITS(4) != Z_DEFLATED) {
-                strm->msg = (char *)"unknown compression method";
+                strm->msg = (z_const char *)"unknown compression method";
                 state->mode = BAD;
                 break;
             }
@@ -656,7 +656,7 @@ int ZEXPORT inflate(z_streamp strm, int flush) {
             if (state->wbits == 0)
                 state->wbits = len;
             if (len > 15 || len > state->wbits) {
-                strm->msg = (char *)"invalid window size";
+                strm->msg = (z_const char *)"invalid window size";
                 state->mode = BAD;
                 break;
             }
@@ -672,12 +672,12 @@ int ZEXPORT inflate(z_streamp strm, int flush) {
             NEEDBITS(16);
             state->flags = (int)(hold);
             if ((state->flags & 0xff) != Z_DEFLATED) {
-                strm->msg = (char *)"unknown compression method";
+                strm->msg = (z_const char *)"unknown compression method";
                 state->mode = BAD;
                 break;
             }
             if (state->flags & 0xe000) {
-                strm->msg = (char *)"unknown header flags set";
+                strm->msg = (z_const char *)"unknown header flags set";
                 state->mode = BAD;
                 break;
             }
@@ -793,7 +793,7 @@ int ZEXPORT inflate(z_streamp strm, int flush) {
             if (state->flags & 0x0200) {
                 NEEDBITS(16);
                 if ((state->wrap & 4) && hold != (state->check & 0xffff)) {
-                    strm->msg = (char *)"header crc mismatch";
+                    strm->msg = (z_const char *)"header crc mismatch";
                     state->mode = BAD;
                     break;
                 }
@@ -855,7 +855,7 @@ int ZEXPORT inflate(z_streamp strm, int flush) {
                 state->mode = TABLE;
                 break;
             case 3:
-                strm->msg = (char *)"invalid block type";
+                strm->msg = (z_const char *)"invalid block type";
                 state->mode = BAD;
             }
             DROPBITS(2);
@@ -864,7 +864,7 @@ int ZEXPORT inflate(z_streamp strm, int flush) {
             BYTEBITS();                         /* go to byte boundary */
             NEEDBITS(32);
             if ((hold & 0xffff) != ((hold >> 16) ^ 0xffff)) {
-                strm->msg = (char *)"invalid stored block lengths";
+                strm->msg = (z_const char *)"invalid stored block lengths";
                 state->mode = BAD;
                 break;
             }
@@ -905,7 +905,7 @@ int ZEXPORT inflate(z_streamp strm, int flush) {
             DROPBITS(4);
 #ifndef PKZIP_BUG_WORKAROUND
             if (state->nlen > 286 || state->ndist > 30) {
-                strm->msg = (char *)"too many length or distance symbols";
+                strm->msg = (z_const char *)"too many length or distance symbols";
                 state->mode = BAD;
                 break;
             }
@@ -928,7 +928,7 @@ int ZEXPORT inflate(z_streamp strm, int flush) {
             ret = inflate_table(CODES, state->lens, 19, &(state->next),
                                 &(state->lenbits), state->work);
             if (ret) {
-                strm->msg = (char *)"invalid code lengths set";
+                strm->msg = (z_const char *)"invalid code lengths set";
                 state->mode = BAD;
                 break;
             }
@@ -952,7 +952,7 @@ int ZEXPORT inflate(z_streamp strm, int flush) {
                         NEEDBITS(here.bits + 2);
                         DROPBITS(here.bits);
                         if (state->have == 0) {
-                            strm->msg = (char *)"invalid bit length repeat";
+                            strm->msg = (z_const char *)"invalid bit length repeat";
                             state->mode = BAD;
                             break;
                         }
@@ -975,7 +975,7 @@ int ZEXPORT inflate(z_streamp strm, int flush) {
                         DROPBITS(7);
                     }
                     if (state->have + copy > state->nlen + state->ndist) {
-                        strm->msg = (char *)"invalid bit length repeat";
+                        strm->msg = (z_const char *)"invalid bit length repeat";
                         state->mode = BAD;
                         break;
                     }
@@ -989,7 +989,7 @@ int ZEXPORT inflate(z_streamp strm, int flush) {
 
             /* check for end-of-block code (better have one) */
             if (state->lens[256] == 0) {
-                strm->msg = (char *)"invalid code -- missing end-of-block";
+                strm->msg = (z_const char *)"invalid code -- missing end-of-block";
                 state->mode = BAD;
                 break;
             }
@@ -1003,7 +1003,7 @@ int ZEXPORT inflate(z_streamp strm, int flush) {
             ret = inflate_table(LENS, state->lens, state->nlen, &(state->next),
                                 &(state->lenbits), state->work);
             if (ret) {
-                strm->msg = (char *)"invalid literal/lengths set";
+                strm->msg = (z_const char *)"invalid literal/lengths set";
                 state->mode = BAD;
                 break;
             }
@@ -1012,7 +1012,7 @@ int ZEXPORT inflate(z_streamp strm, int flush) {
             ret = inflate_table(DISTS, state->lens + state->nlen, state->ndist,
                             &(state->next), &(state->distbits), state->work);
             if (ret) {
-                strm->msg = (char *)"invalid distances set";
+                strm->msg = (z_const char *)"invalid distances set";
                 state->mode = BAD;
                 break;
             }
@@ -1066,7 +1066,7 @@ int ZEXPORT inflate(z_streamp strm, int flush) {
                 break;
             }
             if (here.op & 64) {
-                strm->msg = (char *)"invalid literal/length code";
+                strm->msg = (z_const char *)"invalid literal/length code";
                 state->mode = BAD;
                 break;
             }
@@ -1104,7 +1104,7 @@ int ZEXPORT inflate(z_streamp strm, int flush) {
             DROPBITS(here.bits);
             state->back += here.bits;
             if (here.op & 64) {
-                strm->msg = (char *)"invalid distance code";
+                strm->msg = (z_const char *)"invalid distance code";
                 state->mode = BAD;
                 break;
             }
@@ -1121,7 +1121,7 @@ int ZEXPORT inflate(z_streamp strm, int flush) {
             }
 #ifdef INFLATE_STRICT
             if (state->offset > state->dmax) {
-                strm->msg = (char *)"invalid distance too far back";
+                strm->msg = (z_const char *)"invalid distance too far back";
                 state->mode = BAD;
                 break;
             }
@@ -1136,7 +1136,7 @@ int ZEXPORT inflate(z_streamp strm, int flush) {
                 copy = state->offset - copy;
                 if (copy > state->whave) {
                     if (state->sane) {
-                        strm->msg = (char *)"invalid distance too far back";
+                        strm->msg = (z_const char *)"invalid distance too far back";
                         state->mode = BAD;
                         break;
                     }
@@ -1195,7 +1195,7 @@ int ZEXPORT inflate(z_streamp strm, int flush) {
                      state->flags ? hold :
 #endif
                      ZSWAP32(hold)) != state->check) {
-                    strm->msg = (char *)"incorrect data check";
+                    strm->msg = (z_const char *)"incorrect data check";
                     state->mode = BAD;
                     break;
                 }
@@ -1209,7 +1209,7 @@ int ZEXPORT inflate(z_streamp strm, int flush) {
             if (state->wrap && state->flags) {
                 NEEDBITS(32);
                 if ((state->wrap & 4) && hold != (state->total & 0xffffffff)) {
-                    strm->msg = (char *)"incorrect length check";
+                    strm->msg = (z_const char *)"incorrect length check";
                     state->mode = BAD;
                     break;
                 }