diff --git a/UPGRADING.INTERNALS b/UPGRADING.INTERNALS
index a35c6c70670..10e4ac250b2 100644
--- a/UPGRADING.INTERNALS
+++ b/UPGRADING.INTERNALS
@@ -159,6 +159,7 @@ PHP 8.4 INTERNALS UPGRADE NOTES
    - The HAVE_OPENSSL symbol has been removed.
    - The HAVE_OPENSSL_EXT symbol is now consistently defined to value 1 whether
      the openssl extension is available either as shared or built statically.
+   - Added configure option --enable-phpdbg-debug to build phpdbg in debug mode.
 
 ========================
 3. Module changes
diff --git a/sapi/phpdbg/config.m4 b/sapi/phpdbg/config.m4
index 4a7b1810e90..f8b3315dc63 100644
--- a/sapi/phpdbg/config.m4
+++ b/sapi/phpdbg/config.m4
@@ -8,7 +8,8 @@ PHP_ARG_ENABLE([phpdbg],
 PHP_ARG_ENABLE([phpdbg-debug],
   [for phpdbg debug build],
   [AS_HELP_STRING([--enable-phpdbg-debug],
-    [Build phpdbg in debug mode])],
+    [Build phpdbg in debug mode to enable additional diagnostic output for
+    developing and troubleshooting phpdbg itself])],
   [no],
   [no])
 
@@ -23,13 +24,10 @@ if test "$PHP_PHPDBG" != "no"; then
   AC_HEADER_TIOCGWINSZ
   AC_DEFINE(HAVE_PHPDBG, 1, [ ])
 
-  if test "$PHP_PHPDBG_DEBUG" != "no"; then
-    AC_DEFINE(PHPDBG_DEBUG, 1, [ ])
-  else
-    AC_DEFINE(PHPDBG_DEBUG, 0, [ ])
-  fi
-
   PHP_PHPDBG_CFLAGS="-DZEND_ENABLE_STATIC_TSRMLS_CACHE=1"
+  AS_VAR_IF([PHP_PHPDBG_DEBUG], [no],,
+    [AS_VAR_APPEND([PHP_PHPDBG_CFLAGS], [" -DPHPDBG_DEBUG=1"])])
+
   PHP_PHPDBG_FILES="phpdbg.c phpdbg_parser.c phpdbg_lexer.c phpdbg_prompt.c phpdbg_help.c phpdbg_break.c phpdbg_print.c phpdbg_bp.c phpdbg_list.c phpdbg_utils.c phpdbg_info.c phpdbg_cmd.c phpdbg_set.c phpdbg_frame.c phpdbg_watch.c phpdbg_btree.c phpdbg_sigsafe.c phpdbg_io.c phpdbg_out.c"
 
   AC_MSG_CHECKING([for phpdbg and readline integration])
diff --git a/sapi/phpdbg/config.w32 b/sapi/phpdbg/config.w32
index 06b911c8743..26b6b4b75e4 100644
--- a/sapi/phpdbg/config.w32
+++ b/sapi/phpdbg/config.w32
@@ -1,5 +1,7 @@
 ARG_ENABLE('phpdbg', 'Build phpdbg', 'no');
 ARG_ENABLE('phpdbgs', 'Build phpdbg shared', 'no');
+ARG_ENABLE('phpdbg-debug', 'Build phpdbg in debug mode to enable additional \
+diagnostic output for developing and troubleshooting phpdbg itself', 'no');
 
 PHPDBG_SOURCES='phpdbg.c phpdbg_prompt.c phpdbg_cmd.c phpdbg_info.c phpdbg_help.c phpdbg_break.c ' +
 		'phpdbg_print.c phpdbg_bp.c phpdbg_list.c phpdbg_utils.c ' +
@@ -17,10 +19,18 @@ if (PHP_PHPDBG == "yes") {
 	ADD_FLAG("LIBS_PHPDBG", "ws2_32.lib user32.lib");
 	ADD_FLAG("CFLAGS_PHPDBG", "/D YY_NO_UNISTD_H");
 	ADD_FLAG("LDFLAGS_PHPDBG", "/stack:8388608");
+
+	if(PHP_PHPDBG_DEBUG == "yes") {
+		ADD_FLAG("CFLAGS_PHPDBG", "/D PHPDBG_DEBUG=1");
+	}
 }
 
 if (PHP_PHPDBGS == "yes") {
 	SAPI('phpdbgs', PHPDBG_SOURCES, PHPDBG_DLL, '/D PHP_PHPDBG_EXPORTS');
 	ADD_FLAG("LIBS_PHPDBGS", "ws2_32.lib user32.lib");
 	ADD_FLAG("CFLAGS_PHPDBGS", "/D YY_NO_UNISTD_H");
+
+	if(PHP_PHPDBG_DEBUG == "yes") {
+		ADD_FLAG("CFLAGS_PHPDBGS", "/D PHPDBG_DEBUG=1");
+	}
 }
diff --git a/sapi/phpdbg/phpdbg_out.h b/sapi/phpdbg/phpdbg_out.h
index 828e147a1b7..b99ddaa2e29 100644
--- a/sapi/phpdbg/phpdbg_out.h
+++ b/sapi/phpdbg/phpdbg_out.h
@@ -19,6 +19,10 @@
 #ifndef PHPDBG_OUT_H
 #define PHPDBG_OUT_H
 
+#ifndef PHPDBG_DEBUG
+# define PHPDBG_DEBUG 0
+#endif
+
 /**
  * Error/notice/formatting helpers
  */
diff --git a/win32/build/confutils.js b/win32/build/confutils.js
index 1da17bddbd9..052850bb3d2 100644
--- a/win32/build/confutils.js
+++ b/win32/build/confutils.js
@@ -455,7 +455,8 @@ can be built that way. \
 
 	var snapshot_build_exclusions = new Array(
 		'debug', 'lzf-better-compression', 'php-build', 'snapshot-template', 'zts',
-		'ipv6', 'fd-setsize', 'pgi', 'pgo', 'all-shared', 'config-profile', 'sanitizer'
+		'ipv6', 'fd-setsize', 'pgi', 'pgo', 'all-shared', 'config-profile', 'sanitizer',
+		'phpdbg-debug'
 	);
 	var force;