diff --git a/src/core/nginx.c b/src/core/nginx.c
index 3a413e8..da32c1a 100644
--- a/src/core/nginx.c
+++ b/src/core/nginx.c
@@ -203,9 +203,7 @@
     ngx_cycle_t      *cycle, init_cycle;
     ngx_core_conf_t  *ccf;
 
-#if (NGX_FREEBSD)
     ngx_debug_init();
-#endif
 
     if (ngx_strerror_init() != NGX_OK) {
         return 1;
diff --git a/src/core/ngx_slab.c b/src/core/ngx_slab.c
index 870c59b..9b5b28f 100644
--- a/src/core/ngx_slab.c
+++ b/src/core/ngx_slab.c
@@ -46,10 +46,10 @@
 
 #else
 
-#if (NGX_FREEBSD)
+#if (NGX_HAVE_DEBUG_MALLOC)
 
 #define ngx_slab_junk(p, size)                                                \
-    if (ngx_freebsd_debug_malloc)  ngx_memset(p, 0xD0, size)
+    if (ngx_debug_malloc)          ngx_memset(p, 0xD0, size)
 
 #else
 
diff --git a/src/os/unix/ngx_darwin.h b/src/os/unix/ngx_darwin.h
index 7fa60ff..ebd8d35 100644
--- a/src/os/unix/ngx_darwin.h
+++ b/src/os/unix/ngx_darwin.h
@@ -8,6 +8,7 @@
 #define _NGX_DARWIN_H_INCLUDED_
 
 
+void ngx_debug_init(void);
 ngx_chain_t *ngx_darwin_sendfile_chain(ngx_connection_t *c, ngx_chain_t *in,
     off_t limit);
 
@@ -15,5 +16,7 @@
 extern int       ngx_darwin_hw_ncpu;
 extern u_long    ngx_darwin_net_inet_tcp_sendspace;
 
+extern ngx_uint_t  ngx_debug_malloc;
+
 
 #endif /* _NGX_DARWIN_H_INCLUDED_ */
diff --git a/src/os/unix/ngx_darwin_config.h b/src/os/unix/ngx_darwin_config.h
index a3a14c4..1717c69 100644
--- a/src/os/unix/ngx_darwin_config.h
+++ b/src/os/unix/ngx_darwin_config.h
@@ -87,6 +87,7 @@
 
 
 #define NGX_HAVE_OS_SPECIFIC_INIT    1
+#define NGX_HAVE_DEBUG_MALLOC        1
 
 
 extern char **environ;
diff --git a/src/os/unix/ngx_darwin_init.c b/src/os/unix/ngx_darwin_init.c
index 6713319..c3d1125 100644
--- a/src/os/unix/ngx_darwin_init.c
+++ b/src/os/unix/ngx_darwin_init.c
@@ -14,6 +14,8 @@
 int     ngx_darwin_kern_ipc_somaxconn;
 u_long  ngx_darwin_net_inet_tcp_sendspace;
 
+ngx_uint_t  ngx_debug_malloc;
+
 
 static ngx_os_io_t ngx_darwin_io = {
     ngx_unix_recv,
@@ -55,6 +57,34 @@
 };
 
 
+void
+ngx_debug_init()
+{
+#if (NGX_DEBUG_MALLOC)
+
+    /*
+     * MacOSX 10.6, 10.7:  MallocScribble fills freed memory with 0x55
+     *                     and fills allocated memory with 0xAA.
+     * MacOSX 10.4, 10.5:  MallocScribble fills freed memory with 0x55,
+     *                     MallocPreScribble fills allocated memory with 0xAA.
+     * MacOSX 10.3:        MallocScribble fills freed memory with 0x55,
+     *                     and no way to fill allocated memory.
+     */
+
+    setenv("MallocScribble", "1", 0);
+
+    ngx_debug_malloc = 1;
+
+#else
+
+    if (getenv("MallocScribble")) {
+        ngx_debug_malloc = 1;
+    }
+
+#endif
+}
+
+
 ngx_int_t
 ngx_os_specific_init(ngx_log_t *log)
 {
diff --git a/src/os/unix/ngx_freebsd.h b/src/os/unix/ngx_freebsd.h
index 67fce3e..a96f4eb 100644
--- a/src/os/unix/ngx_freebsd.h
+++ b/src/os/unix/ngx_freebsd.h
@@ -8,6 +8,7 @@
 #define _NGX_FREEBSD_H_INCLUDED_
 
 
+void ngx_debug_init(void);
 ngx_chain_t *ngx_freebsd_sendfile_chain(ngx_connection_t *c, ngx_chain_t *in,
     off_t limit);
 
@@ -17,7 +18,7 @@
 
 extern ngx_uint_t  ngx_freebsd_sendfile_nbytes_bug;
 extern ngx_uint_t  ngx_freebsd_use_tcp_nopush;
-extern ngx_uint_t  ngx_freebsd_debug_malloc;
+extern ngx_uint_t  ngx_debug_malloc;
 
 
 #endif /* _NGX_FREEBSD_H_INCLUDED_ */
diff --git a/src/os/unix/ngx_freebsd_config.h b/src/os/unix/ngx_freebsd_config.h
index 3169c27..798f2ea 100644
--- a/src/os/unix/ngx_freebsd_config.h
+++ b/src/os/unix/ngx_freebsd_config.h
@@ -109,6 +109,7 @@
 
 
 #define NGX_HAVE_OS_SPECIFIC_INIT    1
+#define NGX_HAVE_DEBUG_MALLOC        1
 
 
 extern char **environ;
diff --git a/src/os/unix/ngx_freebsd_init.c b/src/os/unix/ngx_freebsd_init.c
index 1211c7c..bfb8908 100644
--- a/src/os/unix/ngx_freebsd_init.c
+++ b/src/os/unix/ngx_freebsd_init.c
@@ -22,7 +22,8 @@
 
 ngx_uint_t  ngx_freebsd_sendfile_nbytes_bug;
 ngx_uint_t  ngx_freebsd_use_tcp_nopush;
-ngx_uint_t  ngx_freebsd_debug_malloc;
+
+ngx_uint_t  ngx_debug_malloc;
 
 
 static ngx_os_io_t ngx_freebsd_io = {
@@ -80,7 +81,7 @@
     malloc_options = "J";
 #endif
 
-    ngx_freebsd_debug_malloc = 1;
+    ngx_debug_malloc = 1;
 
 #else
     char  *mo;
@@ -88,7 +89,7 @@
     mo = getenv("MALLOC_OPTIONS");
 
     if (mo && ngx_strchr(mo, 'J')) {
-        ngx_freebsd_debug_malloc = 1;
+        ngx_debug_malloc = 1;
     }
 #endif
 }
diff --git a/src/os/unix/ngx_linux_config.h b/src/os/unix/ngx_linux_config.h
index a2ef512..d72cf26 100644
--- a/src/os/unix/ngx_linux_config.h
+++ b/src/os/unix/ngx_linux_config.h
@@ -108,6 +108,7 @@
 
 
 #define NGX_HAVE_OS_SPECIFIC_INIT    1
+#define ngx_debug_init()
 
 
 extern char **environ;
diff --git a/src/os/unix/ngx_os.h b/src/os/unix/ngx_os.h
index f1d8e68..8f9622e 100644
--- a/src/os/unix/ngx_os.h
+++ b/src/os/unix/ngx_os.h
@@ -31,7 +31,6 @@
 } ngx_os_io_t;
 
 
-void ngx_debug_init(void);
 ngx_int_t ngx_os_init(ngx_log_t *log);
 void ngx_os_status(ngx_log_t *log);
 ngx_int_t ngx_os_specific_init(ngx_log_t *log);
diff --git a/src/os/unix/ngx_posix_config.h b/src/os/unix/ngx_posix_config.h
index aec8a0a..e327d54 100644
--- a/src/os/unix/ngx_posix_config.h
+++ b/src/os/unix/ngx_posix_config.h
@@ -125,6 +125,8 @@
 
 #define NGX_LISTEN_BACKLOG  511
 
+#define ngx_debug_init()
+
 
 #if (__FreeBSD__) && (__FreeBSD_version < 400017)
 
diff --git a/src/os/unix/ngx_solaris_config.h b/src/os/unix/ngx_solaris_config.h
index 6b3d42e..fe66026 100644
--- a/src/os/unix/ngx_solaris_config.h
+++ b/src/os/unix/ngx_solaris_config.h
@@ -98,6 +98,7 @@
 
 
 #define NGX_HAVE_OS_SPECIFIC_INIT    1
+#define ngx_debug_init()
 
 
 extern char **environ;
diff --git a/src/os/win32/ngx_win32_config.h b/src/os/win32/ngx_win32_config.h
index 8ffe95c..6d88641 100644
--- a/src/os/win32/ngx_win32_config.h
+++ b/src/os/win32/ngx_win32_config.h
@@ -182,6 +182,7 @@
 
 
 #define ngx_random               rand
+#define ngx_debug_init()
 
 
 #endif /* _NGX_WIN32_CONFIG_H_INCLUDED_ */