diff --git a/src/compiler/config/test/validate-config.spec.ts b/src/compiler/config/test/validate-config.spec.ts
index 81f0bef07ea..1a1060988dd 100644
--- a/src/compiler/config/test/validate-config.spec.ts
+++ b/src/compiler/config/test/validate-config.spec.ts
@@ -293,4 +293,19 @@ describe('validation', () => {
     const { config } = validateConfig(userConfig);
     expect(config.outputTargets.some(o => o.type === 'www')).toBe(true);
   });
+
+  it('should set extras defaults', () => {
+    const { config } = validateConfig(userConfig);
+    expect(config.extras.appendChildSlotFix).toBe(false);
+    expect(config.extras.cloneNodeFix).toBe(false);
+    expect(config.extras.cssVarsShim).toBe(false);
+    expect(config.extras.dynamicImportShim).toBe(false);
+    expect(config.extras.lifecycleDOMEvents).toBe(false);
+    expect(config.extras.safari10).toBe(false);
+    expect(config.extras.scriptDataOpts).toBe(false);
+    expect(config.extras.shadowDomShim).toBe(false);
+    expect(config.extras.slotChildNodesFix).toBe(false);
+    expect(config.extras.initializeNextTick).toBe(false);
+    expect(config.extras.tagNameTransform).toBe(false);
+  });
 });
diff --git a/src/compiler/config/validate-config.ts b/src/compiler/config/validate-config.ts
index 93c363c942c..bfebb2cb9a0 100644
--- a/src/compiler/config/validate-config.ts
+++ b/src/compiler/config/validate-config.ts
@@ -31,14 +31,14 @@ export const validateConfig = (userConfig?: Config) => {
   config.extras = config.extras || {};
   config.extras.appendChildSlotFix = !!config.extras.appendChildSlotFix;
   config.extras.cloneNodeFix = !!config.extras.cloneNodeFix;
-  config.extras.cssVarsShim = config.extras.cssVarsShim !== false;
-  config.extras.dynamicImportShim = config.extras.dynamicImportShim !== false;
+  config.extras.cssVarsShim = !!config.extras.cssVarsShim;
+  config.extras.dynamicImportShim = !!config.extras.dynamicImportShim;
   config.extras.lifecycleDOMEvents = !!config.extras.lifecycleDOMEvents;
-  config.extras.safari10 = config.extras.safari10 !== false;
-  config.extras.scriptDataOpts = config.extras.scriptDataOpts !== false;
-  config.extras.shadowDomShim = config.extras.shadowDomShim !== false;
+  config.extras.safari10 = !!config.extras.safari10;
+  config.extras.scriptDataOpts = !!config.extras.scriptDataOpts;
+  config.extras.shadowDomShim = !!config.extras.shadowDomShim;
   config.extras.slotChildNodesFix = !!config.extras.slotChildNodesFix;
-  config.extras.initializeNextTick = config.extras.initializeNextTick !== false;
+  config.extras.initializeNextTick = !!config.extras.initializeNextTick;
   config.extras.tagNameTransform = !!config.extras.tagNameTransform;
 
   setBooleanConfig(config, 'minifyCss', null, !config.devMode);