diff --git a/src/date-utils.es6 b/src/date-utils.es6
index 75eceb536..3034060cc 100644
--- a/src/date-utils.es6
+++ b/src/date-utils.es6
@@ -12,16 +12,16 @@ const Days = {
   ThisWeekend: 6,
 }
 
-moment.prototype.oclock = function oclock() {
-  return this.minute(0).second(0)
+function oclock(momentDate) {
+  return momentDate.minute(0).second(0)
 }
 
-moment.prototype.morning = function morning(morningHour = Hours.Morning) {
-  return this.hour(morningHour).oclock()
+function morning(momentDate, morningHour = Hours.Morning) {
+  return oclock(momentDate.hour(morningHour))
 }
 
-moment.prototype.evening = function evening(eveningHour = Hours.Evening) {
-  return this.hour(eveningHour).oclock()
+function evening(momentDate, eveningHour = Hours.Evening) {
+  return oclock(momentDate.hour(eveningHour))
 }
 
 
@@ -50,34 +50,34 @@ const DateUtils = {
   },
 
   laterToday(now = moment()) {
-    return now.add(3, 'hours').oclock();
+    return oclock(now.add(3, 'hours'));
   },
 
   tonight(now = moment()) {
     if (now.hour() >= Hours.Evening) {
       return DateUtils.tomorrowEvening();
     }
-    return now.evening();
+    return evening(now)
   },
 
   tomorrow(now = moment()) {
-    return now.add(1, 'day').morning();
+    return morning(now.add(1, 'day'));
   },
 
   tomorrowEvening(now = moment()) {
-    return now.add(1, 'day').evening()
+    return evening(now.add(1, 'day'));
   },
 
   thisWeekend(now = moment()) {
-    return now.day(Days.ThisWeekend).morning()
+    return morning(now.day(Days.ThisWeekend))
   },
 
   nextWeek(now = moment()) {
-    return now.day(Days.NextMonday).morning()
+    return morning(now.day(Days.NextMonday))
   },
 
   nextMonth(now = moment()) {
-    return now.add(1, 'month').date(1).morning()
+    return morning(now.add(1, 'month').date(1))
   },
 
   /**