diff --git a/packages/core/src/render3/definition.ts b/packages/core/src/render3/definition.ts
index 8bc33fd507..1293409123 100644
--- a/packages/core/src/render3/definition.ts
+++ b/packages/core/src/render3/definition.ts
@@ -402,10 +402,12 @@ export function ɵɵsetNgModuleScope(type: any, scope: {
    */
   exports?: Type<any>[] | (() => Type<any>[]);
 }): void {
-  const ngModuleDef = getNgModuleDef(type, true);
-  ngModuleDef.declarations = scope.declarations || EMPTY_ARRAY;
-  ngModuleDef.imports = scope.imports || EMPTY_ARRAY;
-  ngModuleDef.exports = scope.exports || EMPTY_ARRAY;
+  return noSideEffects(() => {
+    const ngModuleDef = getNgModuleDef(type, true);
+    ngModuleDef.declarations = scope.declarations || EMPTY_ARRAY;
+    ngModuleDef.imports = scope.imports || EMPTY_ARRAY;
+    ngModuleDef.exports = scope.exports || EMPTY_ARRAY;
+  }) as never;
 }
 
 /**
diff --git a/packages/core/src/render3/metadata.ts b/packages/core/src/render3/metadata.ts
index e1e1974588..4927c671e0 100644
--- a/packages/core/src/render3/metadata.ts
+++ b/packages/core/src/render3/metadata.ts
@@ -7,6 +7,7 @@
  */
 
 import {Type} from '../interface/type';
+import {noSideEffects} from '../util/closure';
 
 interface TypeWithMetadata extends Type<any> {
   decorators?: any[];
@@ -26,39 +27,41 @@ interface TypeWithMetadata extends Type<any> {
 export function setClassMetadata(
     type: Type<any>, decorators: any[] | null, ctorParameters: (() => any[]) | null,
     propDecorators: {[field: string]: any} | null): void {
-  const clazz = type as TypeWithMetadata;
+  return noSideEffects(() => {
+    const clazz = type as TypeWithMetadata;
 
-  // We determine whether a class has its own metadata by taking the metadata from the parent
-  // constructor and checking whether it's the same as the subclass metadata below. We can't use
-  // `hasOwnProperty` here because it doesn't work correctly in IE10 for static fields that are
-  // defined by TS. See https://github.com/angular/angular/pull/28439#issuecomment-459349218.
-  const parentPrototype = clazz.prototype ? Object.getPrototypeOf(clazz.prototype) : null;
-  const parentConstructor: TypeWithMetadata|null = parentPrototype && parentPrototype.constructor;
+    // We determine whether a class has its own metadata by taking the metadata from the parent
+    // constructor and checking whether it's the same as the subclass metadata below. We can't use
+    // `hasOwnProperty` here because it doesn't work correctly in IE10 for static fields that are
+    // defined by TS. See https://github.com/angular/angular/pull/28439#issuecomment-459349218.
+    const parentPrototype = clazz.prototype ? Object.getPrototypeOf(clazz.prototype) : null;
+    const parentConstructor: TypeWithMetadata|null = parentPrototype && parentPrototype.constructor;
 
-  if (decorators !== null) {
-    if (clazz.decorators !== undefined &&
-        (!parentConstructor || parentConstructor.decorators !== clazz.decorators)) {
-      clazz.decorators.push(...decorators);
-    } else {
-      clazz.decorators = decorators;
+    if (decorators !== null) {
+      if (clazz.decorators !== undefined &&
+          (!parentConstructor || parentConstructor.decorators !== clazz.decorators)) {
+        clazz.decorators.push(...decorators);
+      } else {
+        clazz.decorators = decorators;
+      }
     }
-  }
-  if (ctorParameters !== null) {
-    // Rather than merging, clobber the existing parameters. If other projects exist which use
-    // tsickle-style annotations and reflect over them in the same way, this could cause issues,
-    // but that is vanishingly unlikely.
-    clazz.ctorParameters = ctorParameters;
-  }
-  if (propDecorators !== null) {
-    // The property decorator objects are merged as it is possible different fields have different
-    // decorator types. Decorators on individual fields are not merged, as it's also incredibly
-    // unlikely that a field will be decorated both with an Angular decorator and a non-Angular
-    // decorator that's also been downleveled.
-    if (clazz.propDecorators !== undefined &&
-        (!parentConstructor || parentConstructor.propDecorators !== clazz.propDecorators)) {
-      clazz.propDecorators = {...clazz.propDecorators, ...propDecorators};
-    } else {
-      clazz.propDecorators = propDecorators;
+    if (ctorParameters !== null) {
+      // Rather than merging, clobber the existing parameters. If other projects exist which use
+      // tsickle-style annotations and reflect over them in the same way, this could cause issues,
+      // but that is vanishingly unlikely.
+      clazz.ctorParameters = ctorParameters;
     }
-  }
+    if (propDecorators !== null) {
+      // The property decorator objects are merged as it is possible different fields have different
+      // decorator types. Decorators on individual fields are not merged, as it's also incredibly
+      // unlikely that a field will be decorated both with an Angular decorator and a non-Angular
+      // decorator that's also been downleveled.
+      if (clazz.propDecorators !== undefined &&
+          (!parentConstructor || parentConstructor.propDecorators !== clazz.propDecorators)) {
+        clazz.propDecorators = {...clazz.propDecorators, ...propDecorators};
+      } else {
+        clazz.propDecorators = propDecorators;
+      }
+    }
+  }) as never;
 }