diff --git a/server/month.go b/server/month.go
index bd0c23d..c3fdf2f 100644
--- a/server/month.go
+++ b/server/month.go
@@ -23,16 +23,16 @@ func (m Month) FirstOfMonth() time.Time {
 }
 
 func (m Month) Previous() Month {
-	if m.Month == 1 {
-		return Month{Year: m.Year - 1, Month: 12}
+	if m.Month == int(time.January) {
+		return Month{Year: m.Year - 1, Month: int(time.December)}
 	}
 
 	return Month{Year: m.Year, Month: m.Month - 1}
 }
 
 func (m Month) Next() Month {
-	if m.Month == 12 {
-		return Month{Year: m.Year + 1, Month: 1}
+	if m.Month == int(time.December) {
+		return Month{Year: m.Year + 1, Month: int(time.January)}
 	}
 
 	return Month{Year: m.Year, Month: m.Month + 1}