diff --git a/doc/configuration.txt b/doc/configuration.txt
index c20311d3d..6cb641e49 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -2159,7 +2159,7 @@ tune.zlib.windowsize <number>
 3.3. Debugging
 --------------
 
-debug
+debug (deprecated)
   Enables debug mode which dumps to stdout all exchanges, and disables forking
   into background. It is the equivalent of the command-line argument "-d". It
   should never be used in a production configuration since it may prevent full
diff --git a/src/cfgparse-global.c b/src/cfgparse-global.c
index 3306f8cb8..0e6905976 100644
--- a/src/cfgparse-global.c
+++ b/src/cfgparse-global.c
@@ -57,6 +57,9 @@ int cfg_parse_global(const char *file, int linenum, char **args, int kwm)
 		if (alertif_too_many_args(0, file, linenum, args, &err_code))
 			goto out;
 		global.mode |= MODE_DEBUG;
+		ha_warning("parsing [%s:%d] : '%s' must never be used and will be removed in 2.3. If you need debug mode, please use '-d' on the command line.\n", file, linenum, args[0]);
+		err_code |= ERR_WARN;
+		goto out;
 	}
 	else if (!strcmp(args[0], "noepoll")) {
 		if (alertif_too_many_args(0, file, linenum, args, &err_code))