diff --git a/config/obs/automerge-dependency-collections.json b/config/obs/automerge-dependency-collections.json
index 24082c8..f12ca13 100644
--- a/config/obs/automerge-dependency-collections.json
+++ b/config/obs/automerge-dependency-collections.json
@@ -53,6 +53,21 @@
         "**/pnpm-lock.yaml"
       ]
     },
+    {
+      "id": "terraform",
+      "description": "Terraform/OpenTofu/Terragrunt dependency and lockfile updates",
+      "active": true,
+      "file-glob": [
+        "**/*.tf",
+        "**/*.tfvars",
+        "**/*.tfvars.json",
+        "**/.terraform.lock.hcl",
+        "**/terragrunt.hcl",
+        "**/.opentofu-version",
+        "**/.terraform-version",
+        "**/.terragrunt-version"
+      ]
+    },
     {
       "id": "vm-images",
       "description": "CI runner or container image pin updates",
diff --git a/tests/unit/classifyAutomergeDependencyCollection.test.ts b/tests/unit/classifyAutomergeDependencyCollection.test.ts
index ca78603..cbb7c8e 100644
--- a/tests/unit/classifyAutomergeDependencyCollection.test.ts
+++ b/tests/unit/classifyAutomergeDependencyCollection.test.ts
@@ -96,6 +96,43 @@ test('classifyChangedFiles is ambiguous when multiple collections match', () =>
   assert.equal(outcome.collectionIds.length, 2);
 });
 
+test('classifyChangedFiles allows active terraform collection', () => {
+  const collections = [
+    ...COLLECTIONS,
+    {
+      id: 'terraform',
+      active: true,
+      'file-glob': [
+        '**/*.tf',
+        '**/*.tfvars',
+        '**/*.tfvars.json',
+        '**/.terraform.lock.hcl',
+        '**/terragrunt.hcl',
+        '**/.opentofu-version',
+        '**/.terraform-version',
+        '**/.terragrunt-version',
+      ],
+    },
+  ];
+  const outcome = classifyChangedFiles(
+    [
+      'environments/dev/main.tf',
+      'environments/dev/vars.tfvars',
+      'environments/dev/vars.tfvars.json',
+      'environments/dev/.terraform.lock.hcl',
+      'environments/dev/terragrunt.hcl',
+      'environments/dev/.opentofu-version',
+      'environments/dev/.terraform-version',
+      'environments/dev/.terragrunt-version',
+    ],
+    collections
+  );
+  assert.deepEqual(outcome, {
+    status: 'allowed',
+    collectionId: 'terraform',
+  });
+});
+
 test('buildGateCommentBody includes inactive collection and active list', () => {
   const body = buildGateCommentBody(
     { status: 'inactive', collectionId: 'python-dependencies' },