How can I make this unchecked method invocation checked?

[Dillinger4]

This is driving me crazy. As it stands below the compiler complains that the method invocation is unchecked. If I add a type parameter getMax(Collection<Num> c) the compiler moans that it canno't find symbol method max(java.util.Collection<Num>).

public static Num getMax(Collection c){
 return Collections.max(c); 
}

The method prototype simply suggests that any type can be passed in that extends the type that the Collection is marked to hold.

public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll)