diff --git a/src/recurrence.cpp b/src/recurrence.cpp
--- a/src/recurrence.cpp
+++ b/src/recurrence.cpp
@@ -1361,7 +1361,7 @@
         return;
     }
 
-    d->mRDateTimes.insertSorted(rdate);
+    setInsert(d->mRDateTimes, rdate);
     updated();
 }
 
@@ -1387,7 +1387,7 @@
         return;
     }
 
-    d->mRDates.insertSorted(rdate);
+    setInsert(d->mRDates, rdate);
     updated();
 }
 
@@ -1412,7 +1412,7 @@
         return;
     }
 
-    d->mExDateTimes.insertSorted(exdate);
+    setInsert(d->mExDateTimes, exdate);
     updated();
 }
 
@@ -1442,7 +1442,7 @@
         return;
     }
 
-    d->mExDates.insertSorted(exdate);
+    setInsert(d->mExDates, exdate);
     updated();
 }
 
diff --git a/src/recurrencehelper_p.h b/src/recurrencehelper_p.h
--- a/src/recurrencehelper_p.h
+++ b/src/recurrencehelper_p.h
@@ -45,6 +45,15 @@
     }
 }
 
+template <typename Container, typename Value>
+inline void setInsert(Container &c, const Value &v)
+{
+    const auto it = std::lower_bound(c.begin(), c.end(), v);
+    if (it == c.end() || *it != v) {
+        c.insert(it, v);
+    }
+}
+
 }
 
 #endif