diff --git a/internal/catalog/item_repo.go b/internal/catalog/item_repo.go
index 39dfcfad..c2ebcb23 100644
--- a/internal/catalog/item_repo.go
+++ b/internal/catalog/item_repo.go
@@ -1389,9 +1389,9 @@ func lookupExternalIDsSQL() string {
 			JOIN media_items mi
 			  ON mi.type = $5
 			 AND (
-				(r.provider = 'tmdb' AND mi.tmdb_id = r.provider_id)
-				OR (r.provider = 'tvdb' AND mi.tvdb_id = r.provider_id)
-				OR (r.provider = 'imdb' AND mi.imdb_id = r.provider_id)
+				(r.provider = 'tmdb' AND mi.tmdb_id <> '' AND mi.tmdb_id = r.provider_id)
+				OR (r.provider = 'tvdb' AND mi.tvdb_id <> '' AND mi.tvdb_id = r.provider_id)
+				OR (r.provider = 'imdb' AND mi.imdb_id <> '' AND mi.imdb_id = r.provider_id)
 			 )
 			JOIN media_item_libraries mil ON mil.content_id = mi.content_id
 			JOIN media_folders mf ON mf.id = mil.media_folder_id
diff --git a/internal/catalog/item_repo_test.go b/internal/catalog/item_repo_test.go
index 3e7d8ad8..b8c396ad 100644
--- a/internal/catalog/item_repo_test.go
+++ b/internal/catalog/item_repo_test.go
@@ -199,9 +199,11 @@ func TestLookupExternalIDsSQLChecksProviderTableAndDirectColumns(t *testing.T) {
 		"JOIN media_item_provider_ids mip",
 		"mip.provider = r.provider",
 		"mip.provider_id = r.provider_id",
-		"mi.tmdb_id = r.provider_id",
-		"mi.tvdb_id = r.provider_id",
-		"mi.imdb_id = r.provider_id",
+		"mip.item_type = $5",
+		"mi.type = $5",
+		"mi.tmdb_id <> '' AND mi.tmdb_id = r.provider_id",
+		"mi.tvdb_id <> '' AND mi.tvdb_id = r.provider_id",
+		"mi.imdb_id <> '' AND mi.imdb_id = r.provider_id",
 		"JOIN media_folders mf ON mf.id = mil.media_folder_id",
 		"mf.enabled = true",
 	} {
diff --git a/internal/catalog/provider_id_repo.go b/internal/catalog/provider_id_repo.go
index 264a6ae8..6022f846 100644
--- a/internal/catalog/provider_id_repo.go
+++ b/internal/catalog/provider_id_repo.go
@@ -70,6 +70,36 @@ func (r *ProviderIDRepository) AttachTMDBID(ctx context.Context, contentID, item
 		return fmt.Errorf("media item tmdb id conflict: got %q, want %q", existingTMDBID, tmdbText)
 	}
 
+	var existingProviderTMDBID string
+	err = tx.QueryRow(ctx, `
+		SELECT provider_id
+		FROM media_item_provider_ids
+		WHERE content_id = $1 AND provider = 'tmdb'
+		FOR UPDATE
+	`, contentID).Scan(&existingProviderTMDBID)
+	if err != nil && !errors.Is(err, pgx.ErrNoRows) {
+		return fmt.Errorf("loading media item tmdb provider id: %w", err)
+	}
+	if existingProviderTMDBID != "" && existingProviderTMDBID != tmdbText {
+		return fmt.Errorf("media item tmdb provider id conflict: got %q, want %q", existingProviderTMDBID, tmdbText)
+	}
+
+	var existingOwnerContentID string
+	err = tx.QueryRow(ctx, `
+		SELECT content_id
+		FROM media_items
+		WHERE type = $1
+		  AND tmdb_id = $2
+		  AND content_id <> $3
+		LIMIT 1
+	`, itemType, tmdbText, contentID).Scan(&existingOwnerContentID)
+	if err != nil && !errors.Is(err, pgx.ErrNoRows) {
+		return fmt.Errorf("checking tmdb id owner: %w", err)
+	}
+	if existingOwnerContentID != "" {
+		return fmt.Errorf("tmdb id %q already belongs to content_id %q", tmdbText, existingOwnerContentID)
+	}
+
 	if _, err := tx.Exec(ctx, `
 		UPDATE media_items
 		SET tmdb_id = $1,