diff --git a/src/commonMain/kotlin/de/kif/common/ConstraintChecking.kt b/src/commonMain/kotlin/de/kif/common/ConstraintChecking.kt
index 8f3071c..e0f9bf1 100644
--- a/src/commonMain/kotlin/de/kif/common/ConstraintChecking.kt
+++ b/src/commonMain/kotlin/de/kif/common/ConstraintChecking.kt
@@ -56,6 +56,17 @@ fun checkConstraints(
             }
         }
 
+        for (s in against) {
+            if (
+                schedule != s &&
+                schedule.room.id == s.room.id &&
+                start < s.getAbsoluteEndTime() &&
+                s.getAbsoluteStartTime() < end
+            ) {
+                errors += ConstraintError("Work group cannot be at same time with ${s.workGroup.name} at the same room ${schedule.room.name}!")
+            }
+        }
+
         for ((type, constraints) in schedule.workGroup.constraints.groupBy { it.type }) {
             when (type) {
                 ConstraintType.OnlyOnDay -> {