diff --git a/server/camera_endpoint.py b/server/camera_endpoint.py
index 8bababb..99b801d 100644
--- a/server/camera_endpoint.py
+++ b/server/camera_endpoint.py
@@ -11,7 +11,7 @@ import sqlite3
 from typing import List
 
 from fastapi import Depends
-from pydantic import BaseModel, Field
+from pydantic import BaseModel, Field, model_validator
 
 
 class CameraRecord(BaseModel):
@@ -20,6 +20,12 @@ class CameraRecord(BaseModel):
     entries: int = Field(ge=0)
     exits: int = Field(ge=0)
 
+    @model_validator(mode="after")
+    def _period_order(self):
+        if self.period_end <= self.period_start:
+            raise ValueError("period_end must be strictly greater than period_start")
+        return self
+
 
 class CameraEventsRequest(BaseModel):
     location_id: str
diff --git a/server/test_camera_endpoint.py b/server/test_camera_endpoint.py
index 3917b75..27f00c9 100644
--- a/server/test_camera_endpoint.py
+++ b/server/test_camera_endpoint.py
@@ -98,3 +98,15 @@ def test_negative_counts_rejected():
     with pytest.raises(ValidationError):
         CameraRecord(period_start=1712000000, period_end=1712003600,
                      entries=-1, exits=0)
+
+
+def test_inverted_period_rejected():
+    """Pydantic should reject period_end <= period_start."""
+    from pydantic import ValidationError
+    from server.camera_endpoint import CameraRecord
+    with pytest.raises(ValidationError):
+        CameraRecord(period_start=1712003600, period_end=1712003600,
+                     entries=0, exits=0)
+    with pytest.raises(ValidationError):
+        CameraRecord(period_start=1712003600, period_end=1712000000,
+                     entries=0, exits=0)