diff --git a/lib/config/config.c b/lib/config/config.c
index 1142ed345..db8f3c2c1 100644
--- a/lib/config/config.c
+++ b/lib/config/config.c
@@ -1831,7 +1831,6 @@ static int _out_line_fn(const struct dm_config_node *cn, const char *line, void
 	char version[9];
 	int pos = 0;
 	int space_prefix_len;
-	char *space_prefix;
 	const char *p;
 	size_t len;
 
@@ -1888,10 +1887,9 @@ static int _out_line_fn(const struct dm_config_node *cn, const char *line, void
 	    (cfg_def->flags & (CFG_DEFAULT_UNDEFINED | CFG_DEFAULT_COMMENTED))) {
 		/* print with # at the front to comment out the line */
 		if (_should_print_cfg_with_undef_def_val(out, cfg_def, cn)) {
-			space_prefix = ((len = strspn(line, "\t "))) ? dm_pool_strndup(out->mem, line, len) : NULL;
-			fprintf(out->fp, "%s%s%s\n", space_prefix ? : "", "# ", line + len);
-			if (space_prefix)
-				dm_pool_free(out->mem, space_prefix);
+			space_prefix_len = strspn(line, "\t ");
+			fprintf(out->fp, "%.*s%s%s\n", space_prefix_len, line, "# ",
+				line + space_prefix_len);
 		}
 		return 1;
 	}