diff --git a/packages/common/src/grpc-service.js b/packages/common/src/grpc-service.js
index dc34a30190f..d939832fa23 100644
--- a/packages/common/src/grpc-service.js
+++ b/packages/common/src/grpc-service.js
@@ -757,7 +757,9 @@ GrpcService.prototype.getGrpcCredentials_ = function(callback) {
       grpc.credentials.createFromGoogleCredential(authClient)
     );
 
-    self.projectId = self.projectId || authClient.projectId;
+    if (!self.projectId || self.projectId === '{{projectId}}') {
+      self.projectId = authClient.projectId;
+    }
 
     callback(null, credentials);
   });
diff --git a/packages/common/src/util.js b/packages/common/src/util.js
index 5ac88b61d8b..830d36a07ea 100644
--- a/packages/common/src/util.js
+++ b/packages/common/src/util.js
@@ -493,23 +493,45 @@ function decorateRequest(reqOpts, config) {
     delete reqOpts.json.autoPaginateVal;
   }
 
-  for (var opt in reqOpts) {
-    if (is.string(reqOpts[opt])) {
-      if (reqOpts[opt].indexOf('{{projectId}}') > -1) {
-        if (!config.projectId) {
-          throw util.missingProjectIdError;
-        }
-        reqOpts[opt] = reqOpts[opt].replace(/{{projectId}}/g, config.projectId);
-      }
-    } else if (is.object(reqOpts[opt])) {
-      decorateRequest(reqOpts[opt], config);
+  return util.replaceProjectIdToken(reqOpts, config.projectId);
+}
+
+util.decorateRequest = decorateRequest;
+
+/**
+ * Populate the `{{projectId}}` placeholder.
+ *
+ * @throws {Error} If a projectId is required, but one is not provided.
+ *
+ * @param {*} - Any input value that may contain a placeholder. Arrays and
+ *     objects will be looped.
+ * @param {string} projectId - A projectId. If not provided
+ * @return {*} - The original argument with all placeholders populated.
+ */
+function replaceProjectIdToken(value, projectId) {
+  if (is.array(value)) {
+    value = value.map(function(val) {
+      return replaceProjectIdToken(val, projectId);
+    });
+  }
+
+  if (is.object(value)) {
+    for (var opt in value) {
+      value[opt] = replaceProjectIdToken(value[opt], projectId);
     }
   }
 
-  return reqOpts;
+  if (is.string(value) && value.indexOf('{{projectId}}') > -1) {
+    if (!projectId) {
+      throw util.missingProjectIdError;
+    }
+    value = value.replace(/{{projectId}}/g, projectId);
+  }
+
+  return value;
 }
 
-util.decorateRequest = decorateRequest;
+util.replaceProjectIdToken = replaceProjectIdToken;
 
 /**
  * Extend a global configuration object with user options provided at the time
diff --git a/packages/common/test/grpc-service.js b/packages/common/test/grpc-service.js
index 753cd84a949..6f91b8a847c 100644
--- a/packages/common/test/grpc-service.js
+++ b/packages/common/test/grpc-service.js
@@ -1807,6 +1807,16 @@ describe('GrpcService', function() {
         });
       });
 
+      it('should change placeholder projectId', function(done) {
+        grpcService.projectId = '{{projectId}}';
+
+        grpcService.getGrpcCredentials_(function(err) {
+          assert.ifError(err);
+          assert.strictEqual(grpcService.projectId, AUTH_CLIENT.projectId);
+          done();
+        });
+      });
+
       it('should not update projectId if it was not found', function(done) {
         grpcService.projectId = 'project-id';
 
diff --git a/packages/common/test/util.js b/packages/common/test/util.js
index a904f3e0cc3..00135f2bb79 100644
--- a/packages/common/test/util.js
+++ b/packages/common/test/util.js
@@ -1275,46 +1275,97 @@ describe('common/util', function() {
       assert.strictEqual(decoratedReqOpts.json.autoPaginateVal, undefined);
     });
 
-    describe('projectId placeholder', function() {
-      var PROJECT_ID = 'project-id';
+    it('should decorate the request', function() {
+      var config = {
+        projectId: 'project-id'
+      };
+      var reqOpts = {};
+      var decoratedReqOpts = {};
+
+      utilOverrides.replaceProjectIdToken = function(reqOpts_, projectId) {
+        assert.strictEqual(reqOpts_, reqOpts);
+        assert.strictEqual(projectId, config.projectId);
+        return decoratedReqOpts;
+      };
 
-      it('should replace any {{projectId}} it finds', function() {
-        assert.deepEqual(util.decorateRequest({
+      assert.strictEqual(
+        util.decorateRequest(reqOpts, config),
+        decoratedReqOpts
+      );
+    });
+  });
+
+  describe('projectId placeholder', function() {
+    var PROJECT_ID = 'project-id';
+
+    it('should replace any {{projectId}} it finds', function() {
+      assert.deepEqual(util.replaceProjectIdToken({
+        here: 'A {{projectId}} Z',
+        nested: {
           here: 'A {{projectId}} Z',
           nested: {
+            here: 'A {{projectId}} Z'
+          }
+        },
+        array: [
+          {
             here: 'A {{projectId}} Z',
             nested: {
               here: 'A {{projectId}} Z'
-            }
+            },
+            nestedArray: [
+              {
+                here: 'A {{projectId}} Z',
+                nested: {
+                  here: 'A {{projectId}} Z'
+                }
+              }
+            ]
           }
-        }, { projectId: PROJECT_ID }),
-        {
+        ]
+      }, PROJECT_ID),
+      {
+        here: 'A ' + PROJECT_ID + ' Z',
+        nested: {
           here: 'A ' + PROJECT_ID + ' Z',
           nested: {
+            here: 'A ' + PROJECT_ID + ' Z'
+          }
+        },
+        array: [
+          {
             here: 'A ' + PROJECT_ID + ' Z',
             nested: {
               here: 'A ' + PROJECT_ID + ' Z'
-            }
+            },
+            nestedArray: [
+              {
+                here: 'A ' + PROJECT_ID + ' Z',
+                nested: {
+                  here: 'A ' + PROJECT_ID + ' Z'
+                }
+              }
+            ]
           }
-        });
+        ]
       });
+    });
 
-      it('should replace more than one {{projectId}}', function() {
-        assert.deepEqual(util.decorateRequest({
-          here: 'A {{projectId}} M {{projectId}} Z',
-        }, { projectId: PROJECT_ID }),
-        {
-          here: 'A ' + PROJECT_ID + ' M ' + PROJECT_ID + ' Z'
-        });
+    it('should replace more than one {{projectId}}', function() {
+      assert.deepEqual(util.replaceProjectIdToken({
+        here: 'A {{projectId}} M {{projectId}} Z',
+      }, PROJECT_ID),
+      {
+        here: 'A ' + PROJECT_ID + ' M ' + PROJECT_ID + ' Z'
       });
+    });
 
-      it('should throw if it needs a projectId and cannot find it', function() {
-        assert.throws(function() {
-          util.decorateRequest({
-            here: '{{projectId}}'
-          });
-        }, new RegExp(util.missingProjectIdError));
-      });
+    it('should throw if it needs a projectId and cannot find it', function() {
+      assert.throws(function() {
+        util.replaceProjectIdToken({
+          here: '{{projectId}}'
+        });
+      }, new RegExp(util.missingProjectIdError));
     });
   });