Scala compiler fails to infer the return type when there's an explicit return statement

scala.html.markdown

@@ -199,7 +199,7 @@ weirdSum(2, 4)  // => 16
 
 // The return keyword exists in Scala, but it only returns from the inner-most
 // def that surrounds it. It has no effect on anonymous functions. For example:
-def foo(x: Int) = {
+def foo(x: Int): Int = {
   val anonFunc: Int => Int = { z =>
     if (z > 5)
       return z  // This line makes z the return value of foo!