diff --git a/derp/derp_server.go b/derp/derp_server.go
index 72dcb58c8..23155de1b 100644
--- a/derp/derp_server.go
+++ b/derp/derp_server.go
@@ -653,7 +653,7 @@ func (s *Server) ExpVar() expvar.Var {
 	m.Set("bytes_received", &s.bytesRecv)
 	m.Set("bytes_sent", &s.bytesSent)
 	m.Set("packets_dropped", &s.packetsDropped)
-	m.Set("packets_dropped_reason", &s.packetsDroppedReason)
+	m.Set("counter_packets_dropped_reason", &s.packetsDroppedReason)
 	m.Set("packets_sent", &s.packetsSent)
 	m.Set("packets_received", &s.packetsRecv)
 	m.Set("unknown_frames", &s.unknownFrames)