Index: funcs/func_strings.c
===================================================================
--- funcs/func_strings.c	(revision 18312)
+++ funcs/func_strings.c	(revision 22930)
@@ -1095,6 +1095,7 @@
 {
 	struct ast_var_t *newvar;
 	struct ast_str *prefix = ast_str_alloca(80);
+	size_t buf_len;
 
 	if (!chan) {
 		ast_log(LOG_WARNING, "No channel was provided to %s function.\n", cmd);
@@ -1113,7 +1114,9 @@
 		}
 	}
 	/* Trim the trailing comma */
-	buf[strlen(buf) - 1] = '\0';
+	buf_len = strlen(buf);
+	if (buf_len)
+		buf[buf_len - 1] = '\0';
 	return 0;
 }
 
@@ -1122,6 +1125,7 @@
 	struct ast_var_t *newvar;
 	struct ast_str *prefix = ast_str_alloca(80);
 	char *tmp;
+	size_t buf_len;
 
 	if (!chan) {
 		ast_log(LOG_WARNING, "No channel was provided to %s function.\n", cmd);
@@ -1140,8 +1144,10 @@
 		}
 	}
 	/* Trim the trailing comma */
+	buf_len = ast_str_strlen(*buf);
 	tmp = ast_str_buffer(*buf);
-	tmp[ast_str_strlen(*buf) - 1] = '\0';
+	if (buf_len)
+		tmp[buf_len - 1] = '\0';
 	return 0;
 }