diff --git a/csaf_2_1/mandatoryTests.js b/csaf_2_1/mandatoryTests.js
index 60b53fd3..bf9715a3 100644
--- a/csaf_2_1/mandatoryTests.js
+++ b/csaf_2_1/mandatoryTests.js
@@ -1,6 +1,5 @@
 export {
   mandatoryTest_6_1_3,
-  mandatoryTest_6_1_4,
   mandatoryTest_6_1_5,
   mandatoryTest_6_1_12,
   mandatoryTest_6_1_14,
@@ -32,6 +31,7 @@ export {
 } from '../mandatoryTests.js'
 export { mandatoryTest_6_1_1 } from './mandatoryTests/mandatoryTest_6_1_1.js'
 export { mandatoryTest_6_1_2 } from './mandatoryTests/mandatoryTest_6_1_2.js'
+export { mandatoryTest_6_1_4 } from './mandatoryTests/mandatoryTest_6_1_4.js'
 export { mandatoryTest_6_1_6 } from './mandatoryTests/mandatoryTest_6_1_6.js'
 export { mandatoryTest_6_1_7 } from './mandatoryTests/mandatoryTest_6_1_7.js'
 export { mandatoryTest_6_1_8 } from './mandatoryTests/mandatoryTest_6_1_8.js'
diff --git a/csaf_2_1/mandatoryTests/mandatoryTest_6_1_4.js b/csaf_2_1/mandatoryTests/mandatoryTest_6_1_4.js
new file mode 100644
index 00000000..9e2dc073
--- /dev/null
+++ b/csaf_2_1/mandatoryTests/mandatoryTest_6_1_4.js
@@ -0,0 +1,72 @@
+import { walkPath } from '../../lib/walkPaths.js'
+import {
+  collectGroupIdsFromProductTree,
+  findMissingDefinitions,
+} from './shared/docProductUtils.js'
+
+/**
+ * @typedef {{id: string, instancePath: string}} GroupId
+ */
+
+/**
+ * This implements the mandatory test 6.1.4 of the CSAF 2.1 standard.
+ *
+ * @param {unknown} doc
+ */
+export async function mandatoryTest_6_1_4(doc) {
+  const ctx = {
+    errors:
+      /** @type {Array<{ instancePath: string; message: string }>} */ ([]),
+    isValid: true,
+  }
+
+  const groupIds = collectGroupIdsFromProductTree(/** @type {any} */ (doc))
+  const groupIdRefs = await collectGroupIds(doc)
+  const missingGroupDefinitions =
+    /** @type {{id: string, instancePath: string}[]} */ (
+      findMissingDefinitions(groupIds, groupIdRefs)
+    )
+  if (missingGroupDefinitions.length > 0) {
+    ctx.isValid = false
+    missingGroupDefinitions.forEach(
+      (
+        /** @type {{id: string, instancePath: string}} */ missingGroupDefinition
+      ) => {
+        ctx.errors.push({
+          message: 'definition of group id missing',
+          instancePath: missingGroupDefinition.instancePath,
+        })
+      }
+    )
+  }
+
+  return ctx
+}
+
+/**
+ * Collects all group_id references and their instancePaths from the document.
+ * @param {unknown} doc
+ * @returns {Promise<GroupId[]>}
+ */
+async function collectGroupIds(doc) {
+  const entries = /** @type {GroupId[]} */ ([])
+
+  for (const path of [
+    '/document/notes[]/group_ids[]',
+    '/vulnerabilities[]/first_known_exploitation_dates[]/group_ids[]',
+    '/vulnerabilities[]/flags[]/group_ids[]',
+    '/vulnerabilities[]/ids[]/group_ids[]',
+    '/vulnerabilities[]/involvements[]/group_ids[]',
+    '/vulnerabilities[]/notes[]/group_ids[]',
+    '/vulnerabilities[]/remediations[]/group_ids[]',
+    '/vulnerabilities[]/threats[]/group_ids[]',
+  ]) {
+    await walkPath(doc, path, async (instancePath, value) => {
+      if (typeof value === 'string' && value) {
+        entries.push({ id: value, instancePath })
+      }
+    })
+  }
+
+  return entries
+}
diff --git a/csaf_2_1/mandatoryTests/shared/docProductUtils.js b/csaf_2_1/mandatoryTests/shared/docProductUtils.js
index b73e7947..7e9e776e 100644
--- a/csaf_2_1/mandatoryTests/shared/docProductUtils.js
+++ b/csaf_2_1/mandatoryTests/shared/docProductUtils.js
@@ -30,11 +30,20 @@ const productPathEntrySchema = /** @type {const} */ ({
   },
 })
 
+const productGroupSchema = /** @type {const} */ ({
+  additionalProperties: true,
+  optionalProperties: {
+    group_id: { type: 'string' },
+    summary: { type: 'string' },
+  },
+})
+
 const productTreeSchema = /** @type {const} */ ({
   additionalProperties: true,
   optionalProperties: {
     full_product_names: { elements: fullProductNameSchema },
     product_paths: { elements: productPathEntrySchema },
+    product_groups: { elements: productGroupSchema },
     branches: { elements: branchSchema },
   },
 })
@@ -51,12 +60,14 @@ const inputSchema = /** @type {const} */ ({
  * @typedef {import('ajv/dist/core.js').JTDDataType<typeof branchSchema>} Branch
  * @typedef {import('ajv/dist/core.js').JTDDataType<typeof fullProductNameSchema>} FullProductName
  * @typedef {import('ajv/dist/core.js').JTDDataType<typeof productPathEntrySchema>} ProductPathEntry
+ * @typedef {import('ajv/dist/core.js').JTDDataType<typeof productGroupSchema>} ProductGroup
  */
 
 const validateDoc = ajv.compile(inputSchema)
 
 /**
- * This method collects definitions of product ids and corresponding names and instancePaths in the given document and returns a result object.
+ * This method collects definitions of product ids and corresponding names and
+ * instancePaths in the given document and returns a result object.
  * @param {InputSchema} doc
  * @returns {{id: string, name: string, instancePath: string}[]}
  */
@@ -105,6 +116,46 @@ export const collectProductIdsFromFullProductPath = (doc) => {
   return entries
 }
 
+/**
+ * This method collects definitions of group ids and corresponding names and
+ * instancePaths in the given document and returns a result object.
+ * @param {InputSchema} doc
+ * @returns {{id: string, name: string, instancePath: string}[]}
+ */
+export const collectGroupIdsFromProductTree = (doc) => {
+  const entries =
+    /** @type {{id: string, name: string, instancePath: string}[]} */ ([])
+
+  if (!validateDoc(doc)) {
+    return entries
+  }
+
+  doc.product_tree?.product_groups?.forEach(
+    (productGroup, productGroupIndex) => {
+      if (productGroup.group_id) {
+        entries.push({
+          id: productGroup.group_id,
+          name: productGroup.summary ?? '',
+          instancePath: `/product_tree/product_groups/${productGroupIndex}/group_id`,
+        })
+      }
+    }
+  )
+
+  return entries
+}
+
+/**
+ * Filters a list of references down to those that have no matching definition.
+ * A reference is considered unresolved if no entry in `entries` shares the same `id`.
+ * @param {{id: string}[]} entries
+ * @param {{id: string, instancePath: string}[]} refs
+ * @returns {{id: string, instancePath: string}[]}
+ */
+export const findMissingDefinitions = (entries, refs) => {
+  return refs.filter((ref) => !entries.some((e) => e.id === ref.id))
+}
+
 /**
  * @param {Branch[]} branches
  * @param {{id: string, name: string, instancePath: string}[]} entries
diff --git a/tests/csaf_2_1/oasis.js b/tests/csaf_2_1/oasis.js
index 51e4d5bc..669f3de2 100644
--- a/tests/csaf_2_1/oasis.js
+++ b/tests/csaf_2_1/oasis.js
@@ -87,7 +87,6 @@ const skippedTests = new Set([
   'mandatory/oasis_csaf_tc-csaf_2_1-2024-6-1-03-01.json',
   'mandatory/oasis_csaf_tc-csaf_2_1-2024-6-1-03-02.json',
   'mandatory/oasis_csaf_tc-csaf_2_1-2024-6-1-27-08-02.json',
-  'mandatory/oasis_csaf_tc-csaf_2_1-2024-6-1-04-03.json',
   'recommended/oasis_csaf_tc-csaf_2_1-2024-6-2-38-13.json',
   'recommended/oasis_csaf_tc-csaf_2_1-2024-6-2-38-02.json',
 ])