diff --git a/models/period.cc b/models/period.cc
index 3151efe..92e0156 100644
--- a/models/period.cc
+++ b/models/period.cc
@@ -15,7 +15,7 @@ period::to_json()
 {
     Json::Value result;
 
-    char start_str[6], end_str[6];
+    char start_str[8], end_str[8];
 
     sprintf(start_str, "%02d:%02d", this->start / 60, this->start % 60);
     sprintf(end_str, "%02d:%02d", this->end / 60, this->end % 60);