diff --git a/schema/mysql/schema.sql b/schema/mysql/schema.sql
index 650774d6..755db40c 100644
--- a/schema/mysql/schema.sql
+++ b/schema/mysql/schema.sql
@@ -1142,7 +1142,9 @@ CREATE TABLE user_notification_history (
 
   PRIMARY KEY (id),
 
-  CONSTRAINT fk_user_notification_history_notification_history FOREIGN KEY (notification_history_id) REFERENCES notification_history (id) ON DELETE CASCADE
+  CONSTRAINT fk_user_notification_history_notification_history FOREIGN KEY (notification_history_id) REFERENCES notification_history (id) ON DELETE CASCADE,
+
+  INDEX idx_user_notification_history_notification_history_id (notification_history_id) COMMENT 'Speed up ON DELETE CASCADE'
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin ROW_FORMAT=DYNAMIC;
 
 CREATE TABLE state_history (
diff --git a/schema/mysql/upgrades/1.5.2-pr1059.sql b/schema/mysql/upgrades/1.5.2-pr1059.sql
new file mode 100644
index 00000000..1bfcee5b
--- /dev/null
+++ b/schema/mysql/upgrades/1.5.2-pr1059.sql
@@ -0,0 +1 @@
+ALTER TABLE user_notification_history ADD INDEX idx_user_notification_history_notification_history_id (notification_history_id) COMMENT 'Speed up ON DELETE CASCADE';
diff --git a/schema/pgsql/schema.sql b/schema/pgsql/schema.sql
index f6113469..05617333 100644
--- a/schema/pgsql/schema.sql
+++ b/schema/pgsql/schema.sql
@@ -1840,10 +1840,13 @@ ALTER TABLE user_notification_history ALTER COLUMN environment_id SET STORAGE PL
 ALTER TABLE user_notification_history ALTER COLUMN notification_history_id SET STORAGE PLAIN;
 ALTER TABLE user_notification_history ALTER COLUMN user_id SET STORAGE PLAIN;
 
+CREATE INDEX idx_user_notification_history_notification_history_id ON user_notification_history(notification_history_id);
+
 COMMENT ON COLUMN user_notification_history.id IS 'sha1(notification_history_id + user_id)';
 COMMENT ON COLUMN user_notification_history.environment_id IS 'environment.id';
 COMMENT ON COLUMN user_notification_history.notification_history_id IS 'UUID notification_history.id';
 COMMENT ON COLUMN user_notification_history.user_id IS 'user.id';
+COMMENT ON INDEX idx_user_notification_history_notification_history_id IS 'Speed up ON DELETE CASCADE';
 
 CREATE TABLE state_history (
   id bytea20 NOT NULL,
diff --git a/schema/pgsql/upgrades/1.5.2-pr1059.sql b/schema/pgsql/upgrades/1.5.2-pr1059.sql
new file mode 100644
index 00000000..ec686ad0
--- /dev/null
+++ b/schema/pgsql/upgrades/1.5.2-pr1059.sql
@@ -0,0 +1,2 @@
+CREATE INDEX idx_user_notification_history_notification_history_id ON user_notification_history(notification_history_id);
+COMMENT ON INDEX idx_user_notification_history_notification_history_id IS 'Speed up ON DELETE CASCADE';