diff --git a/packages/@angular/cli/commands/set.ts b/packages/@angular/cli/commands/set.ts
index efeed832f2..1d1111d6d7 100644
--- a/packages/@angular/cli/commands/set.ts
+++ b/packages/@angular/cli/commands/set.ts
@@ -74,8 +74,12 @@ const SetCommand = Command.extend({
         updateLintForPrefix(this.project.root + '/tslint.json', value);
       }
 
-      config.set(jsonPath, value);
-      config.save();
+      try {
+        config.set(jsonPath, value);
+        config.save();
+      } catch (error) {
+        throw new SilentError(error.message);
+      }
       resolve();
     });
   }
diff --git a/packages/@ngtools/json-schema/src/schema-class-factory.ts b/packages/@ngtools/json-schema/src/schema-class-factory.ts
index d932086282..f83bf95d2c 100644
--- a/packages/@ngtools/json-schema/src/schema-class-factory.ts
+++ b/packages/@ngtools/json-schema/src/schema-class-factory.ts
@@ -4,10 +4,8 @@ import {JsonSchemaErrorBase} from './error';
 
 import './mimetypes';
 
-
 export class InvalidJsonPath extends JsonSchemaErrorBase {}
 
-
 // The schema tree node property of the SchemaClass.
 const kSchemaNode = Symbol('schema-node');
 // The value property of the SchemaClass.
@@ -132,6 +130,7 @@ class SchemaClassBase<T> implements SchemaClass<T> {
   /** Set a value from a JSON path. */
   $$set(path: string, value: any): void {
     const node = _getSchemaNodeForPath(this.$$schema(), path);
+
     if (node) {
       node.set(value);
     } else {
diff --git a/packages/@ngtools/json-schema/src/schema-tree.spec.ts b/packages/@ngtools/json-schema/src/schema-tree.spec.ts
index 03726d78d8..fb101763a4 100644
--- a/packages/@ngtools/json-schema/src/schema-tree.spec.ts
+++ b/packages/@ngtools/json-schema/src/schema-tree.spec.ts
@@ -55,12 +55,11 @@ describe('@ngtools/json-schema', () => {
       });
 
       expect(proto.a instanceof Array).toBe(true);
-      expect(proto.a).toEqual([undefined, 'v1', undefined, 'v3']);
+      expect(proto.a).toEqual(['v1', 'v3']);
 
       // Set it to a string, which is valid.
       proto.a[0] = 'v2';
-      proto.a[1] = 'INVALID';
-      expect(proto.a).toEqual(['v2', undefined, undefined, 'v3']);
+      expect(proto.a).toEqual(['v2', 'v3']);
     });
 
     it('supports default values', () => {
@@ -72,6 +71,23 @@ describe('@ngtools/json-schema', () => {
 
       expect(schema.children['b'].get()).toEqual('default');
     });
+
+
+    it('should throw error when setting invalid value', () => {
+      const proto: any = Object.create(null);
+      // tslint:disable-next-line
+      new RootSchemaTreeNode(proto, {
+        value: valueJson,
+        schema: schemaJson
+      });
+
+      try {
+        proto.a[0] = 'INVALID';
+      } catch (error) {
+        expect(error.message).toBe('Invalid value can only be one of these: v1,v2,v3');
+      }
+    });
+
   });
 
 });
diff --git a/packages/@ngtools/json-schema/src/schema-tree.ts b/packages/@ngtools/json-schema/src/schema-tree.ts
index 5f9fef73ad..674e31bb17 100644
--- a/packages/@ngtools/json-schema/src/schema-tree.ts
+++ b/packages/@ngtools/json-schema/src/schema-tree.ts
@@ -7,7 +7,7 @@ export class InvalidSchema extends JsonSchemaErrorBase {}
 export class InvalidValueError extends JsonSchemaErrorBase {}
 export class MissingImplementationError extends JsonSchemaErrorBase {}
 export class SettingReadOnlyPropertyError extends JsonSchemaErrorBase {}
-
+export class InvalidUpdateValue extends JsonSchemaErrorBase {}
 
 export interface Schema {
   [key: string]: any;
@@ -482,6 +482,13 @@ class EnumSchemaTreeNode extends LeafSchemaTreeNode<any> {
 
   get items() { return this._schema['enum']; }
 
+  set(value: string, init = false, force = false) {
+    if (!(value === undefined || this._isInEnum(value))) {
+      throw new InvalidUpdateValue('Invalid value can only be one of these: ' + this.items);
+    }
+    super.set(value, init, force);
+  }
+
   isCompatible(v: any) {
     return this._isInEnum(v);
   }
diff --git a/packages/@ngtools/json-schema/tests/value2-1.json b/packages/@ngtools/json-schema/tests/value2-1.json
index d646965f6f..0bd3cff675 100644
--- a/packages/@ngtools/json-schema/tests/value2-1.json
+++ b/packages/@ngtools/json-schema/tests/value2-1.json
@@ -1,8 +1,6 @@
 {
   "a": [
-    "INVALID",
     "v1",
-    "INVALID",
     "v3"
   ]
 }
diff --git a/tests/e2e/tests/commands/set/set-enum-check.ts b/tests/e2e/tests/commands/set/set-enum-check.ts
new file mode 100644
index 0000000000..33d2847e19
--- /dev/null
+++ b/tests/e2e/tests/commands/set/set-enum-check.ts
@@ -0,0 +1,9 @@
+import {ng} from '../../../utils/process';
+import {expectToFail} from '../../../utils/utils';
+
+export default function() {
+  return Promise.resolve()
+    .then(() => expectToFail(() => ng('set', 'defaults.component.aaa', 'bbb')))
+    .then(() => expectToFail(() => ng('set', 'defaults.component.viewEncapsulation', 'bbb')))
+    .then(() => ng('set', 'defaults.component.viewEncapsulation', 'Emulated'));
+}