diff --git a/modules/@angular/common/src/directives/ng_style.ts b/modules/@angular/common/src/directives/ng_style.ts
index 26a5794808..ed1a21d12b 100644
--- a/modules/@angular/common/src/directives/ng_style.ts
+++ b/modules/@angular/common/src/directives/ng_style.ts
@@ -25,7 +25,7 @@ import {Directive, DoCheck, ElementRef, Input, KeyValueChangeRecord, KeyValueDif
  * @description
  *
  * The styles are updated according to the value of the expression evaluation:
- * - keys are style names with an option `.<unit>` suffix (ie 'top.px', 'font-style.em'),
+ * - keys are style names with an optional `.<unit>` suffix (ie 'top.px', 'font-style.em'),
  * - values are the values assigned to those properties (expressed in the given unit).
  *
  * @stable