diff -r 6a2b0456259a gzlib.c
--- a/gzlib.c	Fri Mar 26 11:41:01 2010 -0700
+++ b/gzlib.c	Fri Mar 26 11:54:06 2010 -0700
@@ -5,7 +5,7 @@
 
 #include "gzguts.h"
 
-#ifdef _LARGEFILE64_SOURCE
+#ifdef ZLIB_LARGEFILE64_SOURCE
 #  define LSEEK lseek64
 #else
 #  define LSEEK lseek
diff -r 6a2b0456259a zconf.h
--- a/zconf.h	Fri Mar 26 11:41:01 2010 -0700
+++ b/zconf.h	Fri Mar 26 11:54:06 2010 -0700
@@ -197,6 +197,17 @@
 #  endif
 #endif
 
+#if defined (__FreeBSD__) || defined (__OpenBSD__) || defined (__NetBSD__) || defined (__APPLE__) || defined(__DragonFly__)
+#  define ZLIB_FILE_OFFSET_BITS 64
+#else
+#  if defined(_FILE_OFFSET_BITS)
+#    define ZLIB_FILE_OFFSET_BITS _FILE_OFFSET_BITS
+#  endif
+#  if defined(_LARGEFILE64_SOURCE)
+#    define ZLIB_LARGEFILE64_SOURCE
+#  endif
+#endif
+
 /* Some Mac compilers merge all .h files incorrectly: */
 #if defined(__MWERKS__)||defined(applec)||defined(THINK_C)||defined(__SC__)
 #  define NO_DUMMY_DECL
@@ -375,7 +386,7 @@
 #  endif
 #endif
 
-#ifdef _LARGEFILE64_SOURCE
+#ifdef ZLIB_LARGEFILE64_SOURCE
 #  include <sys/types.h>
 #endif
 
diff -r 6a2b0456259a zconf.h.in
--- a/zconf.h.in	Fri Mar 26 11:41:01 2010 -0700
+++ b/zconf.h.in	Fri Mar 26 11:54:06 2010 -0700
@@ -197,6 +197,17 @@
 #  endif
 #endif
 
+#if defined (__FreeBSD__) || defined (__OpenBSD__) || defined (__NetBSD__) || defined (__APPLE__) || defined(__DragonFly__)
+#  define ZLIB_FILE_OFFSET_BITS 64
+#else
+#  if defined(_FILE_OFFSET_BITS)
+#    define ZLIB_FILE_OFFSET_BITS _FILE_OFFSET_BITS
+#  endif
+#  if defined(_LARGEFILE64_SOURCE)
+#    define ZLIB_LARGEFILE64_SOURCE
+#  endif
+#endif
+
 /* Some Mac compilers merge all .h files incorrectly: */
 #if defined(__MWERKS__)||defined(applec)||defined(THINK_C)||defined(__SC__)
 #  define NO_DUMMY_DECL
@@ -375,7 +386,7 @@
 #  endif
 #endif
 
-#ifdef _LARGEFILE64_SOURCE
+#ifdef ZLIB_LARGEFILE64_SOURCE
 #  include <sys/types.h>
 #endif
 
diff -r 6a2b0456259a zlib.h
--- a/zlib.h	Fri Mar 26 11:41:01 2010 -0700
+++ b/zlib.h	Fri Mar 26 11:54:06 2010 -0700
@@ -1556,7 +1556,7 @@
         inflateBackInit_((strm), (windowBits), (window), \
                                             ZLIB_VERSION, sizeof(z_stream))
 
-#ifdef _LARGEFILE64_SOURCE
+#ifdef ZLIB_LARGEFILE64_SOURCE
    ZEXTERN gzFile ZEXPORT gzopen64 OF((const char *, const char *));
    ZEXTERN off64_t ZEXPORT gzseek64 OF((gzFile, off64_t, int));
    ZEXTERN off64_t ZEXPORT gztell64 OF((gzFile));
@@ -1565,14 +1565,14 @@
    ZEXTERN uLong ZEXPORT crc32_combine64 OF((uLong, uLong, off64_t));
 #endif
 
-#if !defined(ZLIB_INTERNAL) && _FILE_OFFSET_BITS == 64
+#if !defined(ZLIB_INTERNAL) && ZLIB_FILE_OFFSET_BITS == 64
 #  define gzopen gzopen64
 #  define gzseek gzseek64
 #  define gztell gztell64
 #  define gzoffset gzoffset64
 #  define adler32_combine adler32_combine64
 #  define crc32_combine crc32_combine64
-#  ifndef _LARGEFILE64_SOURCE
+#  ifndef ZLIB_LARGEFILE64_SOURCE
      ZEXTERN gzFile ZEXPORT gzopen64 OF((const char *, const char *));
      ZEXTERN off_t ZEXPORT gzseek64 OF((gzFile, off_t, int));
      ZEXTERN off_t ZEXPORT gztell64 OF((gzFile));