diff --git a/core/projectify/src/index.ts b/core/projectify/src/index.ts
index 2bae22568bc5..1bfe98d433a6 100644
--- a/core/projectify/src/index.ts
+++ b/core/projectify/src/index.ts
@@ -14,6 +14,9 @@ import {Stream} from 'stream';
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+const PROJECT_ID_TOKEN = '{{projectId}}';
+const PROJECT_ID_TOKEN_REGEX = /{{projectId}}/g;
+
 /**
  * Populate the `{{projectId}}` placeholder.
  *
@@ -25,33 +28,43 @@ import {Stream} from 'stream';
  */
 // eslint-disable-next-line  @typescript-eslint/no-explicit-any
 export function replaceProjectIdToken(value: any, projectId: string): any {
-  if (Array.isArray(value)) {
-    value = (value as string[]).map(v => replaceProjectIdToken(v, projectId));
+  if (typeof value === 'string') {
+    if (value.includes(PROJECT_ID_TOKEN)) {
+      if (!projectId || projectId === PROJECT_ID_TOKEN) {
+        throw new MissingProjectIdError();
+      }
+      return value.replace(PROJECT_ID_TOKEN_REGEX, projectId);
+    }
+    return value;
+  }
+
+  if (value === null || typeof value !== 'object') {
+    return value;
   }
 
-  if (
-    value !== null &&
-    typeof value === 'object' &&
-    !(value instanceof Buffer) &&
-    !(value instanceof Stream) &&
-    typeof value.hasOwnProperty === 'function'
-  ) {
-    for (const opt in value) {
-      // eslint-disable-next-line no-prototype-builtins
-      if (value.hasOwnProperty(opt)) {
-        value[opt] = replaceProjectIdToken(value[opt], projectId);
+  if (Array.isArray(value)) {
+    for (let i = 0; i < value.length; i++) {
+      const original = value[i];
+      const processed = replaceProjectIdToken(original, projectId);
+      if (processed !== original) {
+        value[i] = processed;
       }
     }
+    return value;
   }
 
-  if (
-    typeof value === 'string' &&
-    (value as string).indexOf('{{projectId}}') > -1
-  ) {
-    if (!projectId || projectId === '{{projectId}}') {
-      throw new MissingProjectIdError();
+  if (value instanceof Buffer || value instanceof Stream) {
+    return value;
+  }
+
+  for (const key in value) {
+    if (Object.prototype.hasOwnProperty.call(value, key)) {
+      const original = value[key];
+      const processed = replaceProjectIdToken(original, projectId);
+      if (processed !== original) {
+        value[key] = processed;
+      }
     }
-    value = (value as string).replace(/{{projectId}}/g, projectId);
   }
 
   return value;
diff --git a/core/projectify/test/index.ts b/core/projectify/test/index.ts
index b14e2214e39b..8ff9393cc93d 100644
--- a/core/projectify/test/index.ts
+++ b/core/projectify/test/index.ts
@@ -47,6 +47,7 @@ describe('projectId placeholder', () => {
               ],
             },
           ],
+          simpleArray: ['A {{projectId}} Z'],
         },
         PROJECT_ID,
       ),
@@ -74,6 +75,7 @@ describe('projectId placeholder', () => {
             ],
           },
         ],
+        simpleArray: ['A ' + PROJECT_ID + ' Z'],
       },
     );
   });
@@ -116,6 +118,36 @@ describe('projectId placeholder', () => {
     );
   });
 
+  it('should return values without placeholder as-is', () => {
+    assert.strictEqual(
+      replaceProjectIdToken('no-placeholder', PROJECT_ID),
+      'no-placeholder',
+    );
+    assert.strictEqual(replaceProjectIdToken(123, PROJECT_ID), 123);
+    assert.strictEqual(replaceProjectIdToken(true, PROJECT_ID), true);
+    assert.strictEqual(replaceProjectIdToken(null, PROJECT_ID), null);
+    assert.strictEqual(replaceProjectIdToken(undefined, PROJECT_ID), undefined);
+
+    const array = [1, 2, 3];
+    assert.strictEqual(replaceProjectIdToken(array, PROJECT_ID), array);
+
+    const object = {a: 1, b: 2};
+    assert.strictEqual(replaceProjectIdToken(object, PROJECT_ID), object);
+  });
+
+  it('should handle frozen arrays and objects without placeholders correctly without throwing', () => {
+    const frozenArray = Object.freeze(['no-placeholder', 123, true]);
+    const replacedArray = replaceProjectIdToken(frozenArray, PROJECT_ID);
+    assert.strictEqual(frozenArray, replacedArray);
+
+    const frozenObject = Object.freeze({
+      prop: 'no-placeholder',
+      other: 123,
+    });
+    const replacedObject = replaceProjectIdToken(frozenObject, PROJECT_ID);
+    assert.strictEqual(frozenObject, replacedObject);
+  });
+
   it('should not inject projectId into stream', () => {
     // eslint-disable-next-line  @typescript-eslint/no-explicit-any
     const transform = new stream.Transform() as any;