diff --git a/.changeset/hip-experts-dance.md b/.changeset/hip-experts-dance.md
new file mode 100644
index 0000000000..f88fe62cd4
--- /dev/null
+++ b/.changeset/hip-experts-dance.md
@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-catalog-backend': patch
+---
+
+An entity A, that exists in the catalog, can no longer be overwritten by registering a different location that also tries to supply an entity with the same kind+namespace+name. Writes of that new entity will instead be rejected with a log message similar to `Rejecting write of entity Component:default/artist-lookup from file:/Users/freben/dev/github/backstage/packages/catalog-model/examples/components/artist-lookup-component.yaml because entity existed from github:https://github.com/backstage/backstage/blob/master/packages/catalog-model/examples/components/artist-lookup-component.yaml`
diff --git a/plugins/catalog-backend/src/catalog/DatabaseEntitiesCatalog.test.ts b/plugins/catalog-backend/src/catalog/DatabaseEntitiesCatalog.test.ts
index 00898b33a6..8d2138b3e5 100644
--- a/plugins/catalog-backend/src/catalog/DatabaseEntitiesCatalog.test.ts
+++ b/plugins/catalog-backend/src/catalog/DatabaseEntitiesCatalog.test.ts
@@ -15,7 +15,7 @@
  */
 
 import { getVoidLogger } from '@backstage/backend-common';
-import type { Entity } from '@backstage/catalog-model';
+import { Entity, LOCATION_ANNOTATION } from '@backstage/catalog-model';
 import { Database, DatabaseManager, Transaction } from '../database';
 import { EntityFilters } from '../service/EntityFilters';
 import { DatabaseEntitiesCatalog } from './DatabaseEntitiesCatalog';
@@ -127,6 +127,9 @@ describe('DatabaseEntitiesCatalog', () => {
         metadata: {
           name: 'c',
           namespace: 'd',
+          annotations: {
+            [LOCATION_ANNOTATION]: 'mock',
+          },
         },
       };
       const dbEntity: Entity = {
@@ -135,7 +138,11 @@ describe('DatabaseEntitiesCatalog', () => {
         metadata: {
           name: 'c',
           namespace: 'd',
+          description: 'changes',
           uid: 'u',
+          annotations: {
+            [LOCATION_ANNOTATION]: 'mock',
+          },
         },
       };
       db.entities.mockResolvedValue([
diff --git a/plugins/catalog-backend/src/catalog/DatabaseEntitiesCatalog.ts b/plugins/catalog-backend/src/catalog/DatabaseEntitiesCatalog.ts
index 5c55a30a55..f40e327eaa 100644
--- a/plugins/catalog-backend/src/catalog/DatabaseEntitiesCatalog.ts
+++ b/plugins/catalog-backend/src/catalog/DatabaseEntitiesCatalog.ts
@@ -205,9 +205,11 @@ export class DatabaseEntitiesCatalog implements EntitiesCatalog {
                   // TODO(Rugvip): We currently always update relations, but we
                   // likely want to figure out a way to avoid that
                   for (const { entity, relations } of toIgnore) {
-                    const entityId = entity.metadata.uid!;
-                    await this.setRelations(entityId, relations, tx);
-                    modifiedEntityIds.push({ entityId });
+                    const entityId = entity.metadata.uid;
+                    if (entityId) {
+                      await this.setRelations(entityId, relations, tx);
+                      modifiedEntityIds.push({ entityId });
+                    }
                   }
 
                   break;
@@ -300,12 +302,22 @@ export class DatabaseEntitiesCatalog implements EntitiesCatalog {
     for (const request of requests) {
       const newEntity = request.entity;
       const oldEntity = oldEntitiesByName.get(newEntity.metadata.name);
+      const newLocation = newEntity.metadata.annotations?.[LOCATION_ANNOTATION];
+      const oldLocation =
+        oldEntity?.metadata.annotations?.[LOCATION_ANNOTATION];
       if (!oldEntity) {
         toAdd.push(request);
+      } else if (oldLocation !== newLocation) {
+        this.logger.warn(
+          `Rejecting write of entity ${serializeEntityRef(
+            newEntity,
+          )} from ${newLocation} because entity existed from ${oldLocation}`,
+        );
+        toIgnore.push(request);
       } else if (entityHasChanges(oldEntity, newEntity)) {
         // TODO(freben): This currently uses addOrUpdateEntity under the hood,
         // but should probably calculate the end result entity right here
-        // instead and call a dedicated batch update database method instead
+        // instead and call a dedicated batch update database method
         toUpdate.push(request);
       } else {
         toIgnore.push(request);