diff --git a/shiftregister/app/models.py b/shiftregister/app/models.py
index 20f57a5..34bb420 100644
--- a/shiftregister/app/models.py
+++ b/shiftregister/app/models.py
@@ -97,6 +97,40 @@ class Helper(models.Model):
         token.send()
         return token
 
+    def has_overlapping_shift(self, shift):
+        new_shift_end = shift.start_at + shift.duration
+
+        return (
+            ShiftRegistration.objects.annotate(
+                shift_end=ExpressionWrapper(
+                    F("shift__start_at") + F("shift__duration"),
+                    output_field=models.DateTimeField(),
+                )
+            )
+            .filter(
+                helper=self,
+                shift__deleted=False,
+                state__in=[
+                    ShiftRegistration.RegState.REGISTERED,
+                    ShiftRegistration.RegState.CHECKED_IN,
+                ],
+            )
+            .filter(
+                # Case 1: Start time falls between new shift's start and end
+                Q(
+                    shift__start_at__gte=shift.start_at,
+                    shift__start_at__lt=new_shift_end,
+                )
+                |
+                # Case 2: End time falls between new shift's start and end
+                Q(shift_end__gt=shift.start_at, shift_end__lte=new_shift_end)
+                |
+                # Case 3: Completely encompasses the new shift
+                Q(shift__start_at__lte=shift.start_at, shift_end__gte=new_shift_end)
+            )
+            .first()
+        )
+
     # current or next shift
     def important_shift(self):
         ret = (
diff --git a/shiftregister/app/templates/shift.html b/shiftregister/app/templates/shift.html
index f97ad15..9904c73 100644
--- a/shiftregister/app/templates/shift.html
+++ b/shiftregister/app/templates/shift.html
@@ -13,7 +13,11 @@
     <div class="notification">Diese Schicht wurde gelöscht.</div>
 {% endif %}
 {% if not can_register and not is_registered %}
+    {% if has_overlap %}
+    <div class="notification is-warning">Du hast bereits eine überlappende Schicht zu dieser Zeit: <a href="{% url 'shift' overlapping_shift.id %}">{{ overlapping_shift.room.name }} ({{ overlapping_shift.start_at }})</a></div>
+    {% else %}
     <div class="notification">Diese Schicht ist bereits besetzt.</div>
+    {% endif %}
 {% endif %}
     <div class="content">
         <p>
diff --git a/shiftregister/app/views.py b/shiftregister/app/views.py
index 9f268d0..fd94fbb 100644
--- a/shiftregister/app/views.py
+++ b/shiftregister/app/views.py
@@ -211,6 +211,13 @@ def shift(request, shiftid):
             context["can_register"] = False
             if reg[0].can_cancel():
                 context["can_cancel"] = True
+        elif context["can_register"]:
+            # Check for overlapping shifts
+            overlapping_reg = helper.has_overlapping_shift(shift)
+            if overlapping_reg:
+                context["can_register"] = False
+                context["has_overlap"] = True
+                context["overlapping_shift"] = overlapping_reg.shift
 
     if request.method == "POST":
         if EmptyForm(request.POST).is_valid():
@@ -236,6 +243,14 @@ def shift(request, shiftid):
                 )
                 return redirect("index")
             if context["can_register"]:
+                overlapping_reg = helper.has_overlapping_shift(shift)
+                if overlapping_reg:
+                    messages.add_message(
+                        request,
+                        messages.ERROR,
+                        "Du hast bereits eine überlappende Schicht zu dieser Zeit.",
+                    )
+                    return redirect("shift", shiftid=shift.pk)
                 s = ShiftRegistration(helper=helper, shift=shift)
                 s.save()
                 messages.add_message(