iplist/iplist.go      | 11 +++++++++--
 iplist/iplist_test.go | 26 ++++++++++++++++++++++----

diff --git a/iplist/iplist.go b/iplist/iplist.go
index 958af5a94d5fe00897373748e3164e73075cc9f8..93fb9b31ad8bfb7a63e5bcbf90eb18d4d2b04c5b 100644
--- a/iplist/iplist.go
+++ b/iplist/iplist.go
@@ -45,14 +45,21 @@ 	}
 	// TODO: Perhaps all addresses should be converted to IPv6, if the future
 	// of IP is to always be backwards compatible. But this will cost 4x the
 	// memory for IPv4 addresses?
-	if v4 := ip.To4(); v4 != nil {
+	v4 := ip.To4()
+	if v4 != nil {
 		r = me.lookup(v4)
 		if r != nil {
 			return
 		}
 	}
-	if v6 := ip.To16(); v6 != nil {
+	v6 := ip.To16()
+	if v6 != nil {
 		return me.lookup(v6)
+	}
+	if v4 == nil && v6 == nil {
+		return &Range{
+			Description: fmt.Sprintf("unsupported IP: %s", ip),
+		}
 	}
 	return nil
 }
diff --git a/iplist/iplist_test.go b/iplist/iplist_test.go
index 09d216fc2169d66bf2d58f472d5e333958683d50..f21ecc3dbad632730b79adc69e5d4c05e27b1bd7 100644
--- a/iplist/iplist_test.go
+++ b/iplist/iplist_test.go
@@ -73,6 +73,22 @@ 	ret := util.AddrIP(c.RemoteAddr())
 	return ret
 }
 
+func TestBadIP(t *testing.T) {
+	iplist := New(nil)
+	if iplist.Lookup(net.IP(make([]byte, 4))) != nil {
+		t.FailNow()
+	}
+	if iplist.Lookup(net.IP(make([]byte, 16))) != nil {
+		t.FailNow()
+	}
+	if iplist.Lookup(nil) == nil {
+		t.FailNow()
+	}
+	if iplist.Lookup(net.IP(make([]byte, 5))) == nil {
+		t.FailNow()
+	}
+}
+
 func TestSimple(t *testing.T) {
 	ranges, err := sampleRanges(t)
 	if err != nil {
@@ -90,14 +106,16 @@ 	}{
 		{"1.2.3.255", false, ""},
 		{"1.2.8.0", true, "b"},
 		{"1.2.4.255", true, "a"},
-		// Try to roll over to the next octet on the parse.
-		{"1.2.7.256", false, ""},
+		// Try to roll over to the next octet on the parse. Note the final
+		// octet is overbounds. In the next case.
+		{"1.2.7.256", true, "unsupported IP: <nil>"},
 		{"1.2.8.254", true, "b"},
 	} {
-		r := iplist.Lookup(net.ParseIP(_case.IP))
+		ip := net.ParseIP(_case.IP)
+		r := iplist.Lookup(ip)
 		if !_case.Hit {
 			if r != nil {
-				t.Fatalf("got hit when none was expected")
+				t.Fatalf("got hit when none was expected: %s", ip)
 			}
 			continue
 		}