diff --git i/honeypot.install w/honeypot.install
index e924595..fd4d345 100644
--- i/honeypot.install
+++ w/honeypot.install
@@ -15,6 +15,12 @@ function honeypot_schema() {
   $schema['honeypot_user'] = [
     'description' => 'Table that stores failed attempts to submit a form.',
     'fields' => [
+      'id' => [
+        'description' => 'Primary key.',
+        'type' => 'serial',
+        'unsigned' => TRUE,
+        'not null' => TRUE,
+      ],
       'uid' => [
         'description' => 'Foreign key to {users}.uid; uniquely identifies a Drupal user to whom this ACL data applies.',
         'type' => 'int',
@@ -34,6 +40,7 @@ function honeypot_schema() {
         'not null' => TRUE,
       ],
     ],
+    'primary key' => ['id'],
     'indexes' => [
       'uid' => ['uid'],
       'timestamp' => ['timestamp'],
@@ -72,3 +79,20 @@ function honeypot_update_8100() {
   $spec['initial'] = '';
   \Drupal::database()->schema()->addField('honeypot_user', 'hostname', $spec);
 }
+
+/**
+ * Adds the 'id' column to the {honeypot_user} table.
+ */
+function honeypot_update_8101() {
+  $schema = \Drupal::database()->schema();
+
+  if (!$schema->fieldExists('honeypot_user', 'id')) {
+    $spec = [
+      'description' => 'Primary key.',
+      'type' => 'serial',
+      'unsigned' => TRUE,
+      'not null' => TRUE,
+    ];
+    $schema->addField('honeypot_user', 'id', $spec, ['primary key' => ['id']]);
+  }
+}