diff --git a/Makefile.in b/Makefile.in
index 67592f3..f608c6c 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -20,7 +20,7 @@ CC=cc
 
 CFLAGS=-O
 #CFLAGS=-O -DMAX_WBITS=14 -DMAX_MEM_LEVEL=7
-#CFLAGS=-g -DDEBUG
+#CFLAGS=-g -DZLIB_DEBUG
 #CFLAGS=-O3 -Wall -Wwrite-strings -Wpointer-arith -Wconversion \
 #           -Wstrict-prototypes -Wmissing-prototypes
 
diff --git a/deflate.c b/deflate.c
index aeabbae..7a9e05e 100644
--- a/deflate.c
+++ b/deflate.c
@@ -92,7 +92,7 @@ local int read_buf        OF((z_streamp strm, Bytef *buf, unsigned size));
 local uInt longest_match  OF((deflate_state *s, IPos cur_match));
 #endif
 
-#ifdef DEBUG
+#ifdef ZLIB_DEBUG
 local  void check_match OF((deflate_state *s, IPos start, IPos match,
                             int length));
 #endif
@@ -1349,7 +1349,7 @@ local uInt longest_match(s, cur_match)
 
 #endif /* FASTEST */
 
-#ifdef DEBUG
+#ifdef ZLIB_DEBUG
 /* ===========================================================================
  * Check that the match at match_start is indeed a match.
  */
@@ -1375,7 +1375,7 @@ local void check_match(s, start, match, length)
 }
 #else
 #  define check_match(s, start, match, length)
-#endif /* DEBUG */
+#endif /* ZLIB_DEBUG */
 
 /* ===========================================================================
  * Fill the window when the lookahead becomes insufficient.
diff --git a/deflate.h b/deflate.h
index ce0299e..8440790 100644
--- a/deflate.h
+++ b/deflate.h
@@ -249,7 +249,7 @@ typedef struct internal_state {
     uInt matches;       /* number of string matches in current block */
     uInt insert;        /* bytes at end of window left to insert */
 
-#ifdef DEBUG
+#ifdef ZLIB_DEBUG
     ulg compressed_len; /* total bit length of compressed file mod 2^32 */
     ulg bits_sent;      /* bit length of compressed data sent mod 2^32 */
 #endif
@@ -309,7 +309,7 @@ void ZLIB_INTERNAL _tr_stored_block OF((deflate_state *s, charf *buf,
  * used.
  */
 
-#ifndef DEBUG
+#ifndef ZLIB_DEBUG
 /* Inline versions of _tr_tally for speed: */
 
 #if defined(GEN_TREES_H) || !defined(STDC)
diff --git a/examples/gzlog.c b/examples/gzlog.c
index 922f878..f33a862 100644
--- a/examples/gzlog.c
+++ b/examples/gzlog.c
@@ -243,7 +243,7 @@ typedef unsigned int uint;
 typedef unsigned long ulong;
 
 /* Macro for debugging to deterministically force recovery operations */
-#ifdef DEBUG
+#ifdef GZLOG_DEBUG
     #include <setjmp.h>         /* longjmp */
     jmp_buf gzlog_jump;         /* where to go back to */
     int gzlog_bail = 0;         /* which point to bail at (1..8) */
diff --git a/msdos/Makefile.dj2 b/msdos/Makefile.dj2
index 29b0395..59d2037 100644
--- a/msdos/Makefile.dj2
+++ b/msdos/Makefile.dj2
@@ -29,7 +29,7 @@ CC=gcc
 
 #CFLAGS=-MMD -O
 #CFLAGS=-O -DMAX_WBITS=14 -DMAX_MEM_LEVEL=7
-#CFLAGS=-MMD -g -DDEBUG
+#CFLAGS=-MMD -g -DZLIB_DEBUG
 CFLAGS=-MMD -O3 $(BUTT) -Wall -Wwrite-strings -Wpointer-arith -Wconversion \
              -Wstrict-prototypes -Wmissing-prototypes
 
diff --git a/msdos/Makefile.emx b/msdos/Makefile.emx
index 9c1b57a..e30f67b 100644
--- a/msdos/Makefile.emx
+++ b/msdos/Makefile.emx
@@ -11,7 +11,7 @@ CC=gcc
 
 #CFLAGS=-MMD -O
 #CFLAGS=-O -DMAX_WBITS=14 -DMAX_MEM_LEVEL=7
-#CFLAGS=-MMD -g -DDEBUG
+#CFLAGS=-MMD -g -DZLIB_DEBUG
 CFLAGS=-MMD -O3 $(BUTT) -Wall -Wwrite-strings -Wpointer-arith -Wconversion \
              -Wstrict-prototypes -Wmissing-prototypes
 
diff --git a/old/Makefile.emx b/old/Makefile.emx
index 4d6ab0e..612b037 100644
--- a/old/Makefile.emx
+++ b/old/Makefile.emx
@@ -11,7 +11,7 @@ CC=gcc -Zwin32
 
 #CFLAGS=-MMD -O
 #CFLAGS=-O -DMAX_WBITS=14 -DMAX_MEM_LEVEL=7
-#CFLAGS=-MMD -g -DDEBUG
+#CFLAGS=-MMD -g -DZLIB_DEBUG
 CFLAGS=-MMD -O3 $(BUTT) -Wall -Wwrite-strings -Wpointer-arith -Wconversion \
              -Wstrict-prototypes -Wmissing-prototypes
 
diff --git a/old/os2/Makefile.os2 b/old/os2/Makefile.os2
index a105aaa..bb426c0 100644
--- a/old/os2/Makefile.os2
+++ b/old/os2/Makefile.os2
@@ -14,7 +14,7 @@ CC=gcc -Zomf -s
 
 CFLAGS=-O6 -Wall
 #CFLAGS=-O -DMAX_WBITS=14 -DMAX_MEM_LEVEL=7
-#CFLAGS=-g -DDEBUG
+#CFLAGS=-g -DZLIB_DEBUG
 #CFLAGS=-O3 -Wall -Wwrite-strings -Wpointer-arith -Wconversion \
 #           -Wstrict-prototypes -Wmissing-prototypes
 
diff --git a/treebuild.xml b/treebuild.xml
index 7a8ea27..d3732d8 100644
--- a/treebuild.xml
+++ b/treebuild.xml
@@ -101,7 +101,7 @@
 <!--
 CFLAGS=-O
 #CFLAGS=-O -DMAX_WBITS=14 -DMAX_MEM_LEVEL=7
-#CFLAGS=-g -DDEBUG
+#CFLAGS=-g -DZLIB_DEBUG
 #CFLAGS=-O3 -Wall -Wwrite-strings -Wpointer-arith -Wconversion \
 #           -Wstrict-prototypes -Wmissing-prototypes
 
diff --git a/trees.c b/trees.c
index 1fd7759..ad37628 100644
--- a/trees.c
+++ b/trees.c
@@ -36,7 +36,7 @@
 
 #include "deflate.h"
 
-#ifdef DEBUG
+#ifdef ZLIB_DEBUG
 #  include <ctype.h>
 #endif
 
@@ -159,11 +159,11 @@ local void copy_block     OF((deflate_state *s, charf *buf, unsigned len,
 local void gen_trees_header OF((void));
 #endif
 
-#ifndef DEBUG
+#ifndef ZLIB_DEBUG
 #  define send_code(s, c, tree) send_bits(s, tree[c].Code, tree[c].Len)
    /* Send a code of the given tree. c and tree must not have side effects */
 
-#else /* DEBUG */
+#else /* !ZLIB_DEBUG */
 #  define send_code(s, c, tree) \
      { if (z_verbose>2) fprintf(stderr,"\ncd %3d ",(c)); \
        send_bits(s, tree[c].Code, tree[c].Len); }
@@ -182,7 +182,7 @@ local void gen_trees_header OF((void));
  * Send a value on a given number of bits.
  * IN assertion: length <= 16 and value fits in length bits.
  */
-#ifdef DEBUG
+#ifdef ZLIB_DEBUG
 local void send_bits      OF((deflate_state *s, int value, int length));
 
 local void send_bits(s, value, length)
@@ -208,7 +208,7 @@ local void send_bits(s, value, length)
         s->bi_valid += length;
     }
 }
-#else /* !DEBUG */
+#else /* !ZLIB_DEBUG */
 
 #define send_bits(s, value, length) \
 { int len = length;\
@@ -223,7 +223,7 @@ local void send_bits(s, value, length)
     s->bi_valid += len;\
   }\
 }
-#endif /* DEBUG */
+#endif /* ZLIB_DEBUG */
 
 
 /* the arguments must not have side effects */
@@ -317,7 +317,7 @@ local void tr_static_init()
  * Genererate the file trees.h describing the static trees.
  */
 #ifdef GEN_TREES_H
-#  ifndef DEBUG
+#  ifndef ZLIB_DEBUG
 #    include <stdio.h>
 #  endif
 
@@ -394,7 +394,7 @@ void ZLIB_INTERNAL _tr_init(s)
 
     s->bi_buf = 0;
     s->bi_valid = 0;
-#ifdef DEBUG
+#ifdef ZLIB_DEBUG
     s->compressed_len = 0L;
     s->bits_sent = 0L;
 #endif
@@ -869,7 +869,7 @@ void ZLIB_INTERNAL _tr_stored_block(s, buf, stored_len, last)
     int last;         /* one if this is the last block for a file */
 {
     send_bits(s, (STORED_BLOCK<<1)+last, 3);    /* send block type */
-#ifdef DEBUG
+#ifdef ZLIB_DEBUG
     s->compressed_len = (s->compressed_len + 3 + 7) & (ulg)~7L;
     s->compressed_len += (stored_len + 4) << 3;
 #endif
@@ -894,7 +894,7 @@ void ZLIB_INTERNAL _tr_align(s)
 {
     send_bits(s, STATIC_TREES<<1, 3);
     send_code(s, END_BLOCK, static_ltree);
-#ifdef DEBUG
+#ifdef ZLIB_DEBUG
     s->compressed_len += 10L; /* 3 for block type, 7 for EOB */
 #endif
     bi_flush(s);
@@ -974,7 +974,7 @@ void ZLIB_INTERNAL _tr_flush_block(s, buf, stored_len, last)
         send_bits(s, (STATIC_TREES<<1)+last, 3);
         compress_block(s, (const ct_data *)static_ltree,
                        (const ct_data *)static_dtree);
-#ifdef DEBUG
+#ifdef ZLIB_DEBUG
         s->compressed_len += 3 + s->static_len;
 #endif
     } else {
@@ -983,7 +983,7 @@ void ZLIB_INTERNAL _tr_flush_block(s, buf, stored_len, last)
                        max_blindex+1);
         compress_block(s, (const ct_data *)s->dyn_ltree,
                        (const ct_data *)s->dyn_dtree);
-#ifdef DEBUG
+#ifdef ZLIB_DEBUG
         s->compressed_len += 3 + s->opt_len;
 #endif
     }
@@ -995,7 +995,7 @@ void ZLIB_INTERNAL _tr_flush_block(s, buf, stored_len, last)
 
     if (last) {
         bi_windup(s);
-#ifdef DEBUG
+#ifdef ZLIB_DEBUG
         s->compressed_len += 7;  /* align on byte boundary */
 #endif
     }
@@ -1193,7 +1193,7 @@ local void bi_windup(s)
     }
     s->bi_buf = 0;
     s->bi_valid = 0;
-#ifdef DEBUG
+#ifdef ZLIB_DEBUG
     s->bits_sent = (s->bits_sent+7) & ~7;
 #endif
 }
@@ -1213,11 +1213,11 @@ local void copy_block(s, buf, len, header)
     if (header) {
         put_short(s, (ush)len);
         put_short(s, (ush)~len);
-#ifdef DEBUG
+#ifdef ZLIB_DEBUG
         s->bits_sent += 2*16;
 #endif
     }
-#ifdef DEBUG
+#ifdef ZLIB_DEBUG
     s->bits_sent += (ulg)len<<3;
 #endif
     while (len--) {
diff --git a/win32/Makefile.gcc b/win32/Makefile.gcc
index 6d1ded6..305be50 100644
--- a/win32/Makefile.gcc
+++ b/win32/Makefile.gcc
@@ -39,7 +39,7 @@ IMPLIB    = libz.dll.a
 SHARED_MODE=0
 
 #LOC = -DASMV
-#LOC = -DDEBUG -g
+#LOC = -DZLIB_DEBUG -g
 
 PREFIX =
 CC = $(PREFIX)gcc
diff --git a/zlib.h b/zlib.h
index 0681f6f..c563014 100644
--- a/zlib.h
+++ b/zlib.h
@@ -1122,7 +1122,7 @@ ZEXTERN uLong ZEXPORT zlibCompileFlags OF((void));
      7.6: size of z_off_t
 
     Compiler, assembler, and debug options:
-     8: DEBUG
+     8: ZLIB_DEBUG
      9: ASMV or ASMINF -- use ASM code
      10: ZLIB_WINAPI -- exported functions use the WINAPI calling convention
      11: 0 (reserved)
diff --git a/zutil.c b/zutil.c
index 23d2ebe..15add3b 100644
--- a/zutil.c
+++ b/zutil.c
@@ -61,7 +61,7 @@ uLong ZEXPORT zlibCompileFlags()
     case 8:     flags += 2 << 6;        break;
     default:    flags += 3 << 6;
     }
-#ifdef DEBUG
+#ifdef ZLIB_DEBUG
     flags += 1 << 8;
 #endif
 #if defined(ASMV) || defined(ASMINF)
@@ -115,7 +115,7 @@ uLong ZEXPORT zlibCompileFlags()
     return flags;
 }
 
-#ifdef DEBUG
+#ifdef ZLIB_DEBUG
 
 #  ifndef verbose
 #    define verbose 0
diff --git a/zutil.h b/zutil.h
index 24ab06b..3b761d3 100644
--- a/zutil.h
+++ b/zutil.h
@@ -216,7 +216,7 @@ extern z_const char * const z_errmsg[10]; /* indexed by 2-zlib_error */
 #endif
 
 /* Diagnostic functions */
-#ifdef DEBUG
+#ifdef ZLIB_DEBUG
 #  include <stdio.h>
    extern int ZLIB_INTERNAL z_verbose;
    extern void ZLIB_INTERNAL z_error OF((char *m));