--- a/src/cmp.rs	Fri Aug 18 06:18:25 2017 +0000
+++ b/src/cmp.rs	Wed Aug 23 19:09:22 2017 +0200
@@ -121,6 +121,13 @@
     }
 }
 
+impl InternalKeyCmp {
+    /// cmp_inner compares a and b using the underlying comparator (the "user comparator").
+    fn cmp_inner(&self, a: &[u8], b: &[u8]) -> Ordering {
+        self.0.cmp(a, b)
+    }
+}
+
 /// An internal comparator wrapping a user-supplied comparator. This comparator is used to compare
 /// memtable keys, which contain length prefixes and a sequence number.
 /// The ordering is determined by asking the wrapped comparator; ties are broken by *reverse*
@@ -249,6 +256,24 @@
     }
 
     #[test]
+    fn test_cmp_internalkeycmp() {
+        let cmp = InternalKeyCmp(Arc::new(Box::new(DefaultCmp)));
+        // a < b < c
+        let a = LookupKey::new("abc".as_bytes(), 2).internal_key().to_vec();
+        let b = LookupKey::new("abc".as_bytes(), 1).internal_key().to_vec();
+        let c = LookupKey::new("abd".as_bytes(), 3).internal_key().to_vec();
+        let d = "xyy".as_bytes();
+        let e = "xyz".as_bytes();
+
+        assert_eq!(Ordering::Less, cmp.cmp(&a, &b));
+        assert_eq!(Ordering::Equal, cmp.cmp(&a, &a));
+        assert_eq!(Ordering::Greater, cmp.cmp(&b, &a));
+        assert_eq!(Ordering::Less, cmp.cmp(&a, &c));
+        assert_eq!(Ordering::Less, cmp.cmp_inner(d, e));
+        assert_eq!(Ordering::Greater, cmp.cmp_inner(e, d));
+    }
+
+    #[test]
     #[should_panic]
     fn test_cmp_memtablekeycmp_panics() {
         let cmp = MemtableKeyCmp(Arc::new(Box::new(DefaultCmp)));