diff --git a/doc/go_spec.html b/doc/go_spec.html
index 7ad90dd129..13af1d83a1 100644
--- a/doc/go_spec.html
+++ b/doc/go_spec.html
@@ -1696,7 +1696,7 @@ of an interface type or of elements of a composite type remains unchanged:
 </p>
 
 <pre>
-// A Mutex is a data type with two methods Lock and Unlock.
+// A Mutex is a data type with two methods, Lock and Unlock.
 type Mutex struct         { /* Mutex fields */ }
 func (m *Mutex) Lock()    { /* Lock implementation */ }
 func (m *Mutex) Unlock()  { /* Unlock implementation */ }