diff --git a/ui/styling/style.ts b/ui/styling/style.ts
index fcb8c3504..fdabfaf09 100644
--- a/ui/styling/style.ts
+++ b/ui/styling/style.ts
@@ -470,10 +470,18 @@ export var fontFamilyProperty = new styleProperty.Property("fontFamily", "font-f
     new observable.PropertyMetadata(undefined, observable.PropertyMetadataSettings.Inheritable, onFontFamilyChanged));
 
 export var fontStyleProperty = new styleProperty.Property("fontStyle", "font-style",
-    new observable.PropertyMetadata(undefined, observable.PropertyMetadataSettings.Inheritable, onFontStyleChanged));
+    new observable.PropertyMetadata(undefined, observable.PropertyMetadataSettings.Inheritable, onFontStyleChanged, isFontStyleValid));
 
 export var fontWeightProperty = new styleProperty.Property("fontWeight", "font-weight",
-    new observable.PropertyMetadata(undefined, observable.PropertyMetadataSettings.Inheritable, onFontWeightChanged));
+    new observable.PropertyMetadata(undefined, observable.PropertyMetadataSettings.Inheritable, onFontWeightChanged, isFontWeightValid));
+
+function isFontWeightValid(value: string): boolean {
+    return value === enums.FontWeight.normal || value === enums.FontWeight.bold;
+}
+
+function isFontStyleValid(value: string): boolean {
+    return value === enums.FontStyle.normal || value === enums.FontStyle.italic;
+}
 
 function onFontFamilyChanged(data: observable.PropertyChangeData) {
     var style = <Style>data.object;
diff --git a/ui/styling/stylers.android.ts b/ui/styling/stylers.android.ts
index 3e90a4ae4..17522e907 100644
--- a/ui/styling/stylers.android.ts
+++ b/ui/styling/stylers.android.ts
@@ -512,6 +512,7 @@ export class BorderStyler implements definition.stylers.Styler {
     }
 }
 
+// Register all styler at the end.
 export function _registerDefaultStylers() {
     style.registerNoStylingClass("Frame");
     DefaultStyler.registerHandlers();
diff --git a/ui/styling/stylers.ios.ts b/ui/styling/stylers.ios.ts
index d549a9814..6a25a5d1f 100644
--- a/ui/styling/stylers.ios.ts
+++ b/ui/styling/stylers.ios.ts
@@ -619,17 +619,6 @@ export class SearchBarStyler implements definition.stylers.Styler {
     }
 }
 
-export function _registerDefaultStylers() {
-    style.registerNoStylingClass("Frame");
-    DefaultStyler.registerHandlers();
-    ButtonStyler.registerHandlers();
-    LabelStyler.registerHandlers();
-    TextFieldStyler.registerHandlers();
-    TextViewStyler.registerHandlers();
-    SegmentedBarStyler.registerHandlers();
-    SearchBarStyler.registerHandlers();
-}
-
 interface ViewWithFont {
     font: UIFont;
 }
@@ -675,3 +664,15 @@ function resetFont(view: ViewWithFont, newValue: UIFont) {
 function getNativeFont(view: ViewWithFont): UIFont {
     return view.font;
 }
+
+// Register all styler at the end.
+export function _registerDefaultStylers() {
+    style.registerNoStylingClass("Frame");
+    DefaultStyler.registerHandlers();
+    ButtonStyler.registerHandlers();
+    LabelStyler.registerHandlers();
+    TextFieldStyler.registerHandlers();
+    TextViewStyler.registerHandlers();
+    SegmentedBarStyler.registerHandlers();
+    SearchBarStyler.registerHandlers();
+}
\ No newline at end of file