diff --git a/mu-prometheus.cabal b/mu-prometheus.cabal
--- a/mu-prometheus.cabal
+++ b/mu-prometheus.cabal
@@ -1,9 +1,7 @@
 name:          mu-prometheus
-version:       0.4.0.0
+version:       0.5.0.0
 synopsis:      Metrics support for Mu using Prometheus
-description:
-  Get metrics of your running Mu servers using Prometheus
-
+description:   Get metrics of your running Mu servers using Prometheus
 license:       Apache-2.0
 license-file:  LICENSE
 author:        Alejandro Serrano
@@ -20,18 +18,16 @@
   location: https://github.com/higherkindness/mu-haskell
 
 library
-  exposed-modules:
-    Mu.Instrumentation.Prometheus
-
+  exposed-modules:  Mu.Instrumentation.Prometheus
   build-depends:
-      base                  >=4.12 && <5
-    , lifted-base           >=0.2  && <0.3
-    , monad-control         >1     && <2
-    , mu-rpc                ==0.4.*
-    , prometheus-client     >1     && <2
-    , text                  >=1.2  && <2
-    , wai                   >=3.2  && <4
-    , wai-middleware-prometheus >1 && <2
+      base                       >=4.12 && <5
+    , lifted-base                >=0.2  && <0.3
+    , monad-control              >1     && <2
+    , mu-rpc                     >=0.5  && <0.6
+    , prometheus-client          >1     && <2
+    , text                       >=1.2  && <2
+    , wai                        >=3.2  && <4
+    , wai-middleware-prometheus  >1     && <2
 
   hs-source-dirs:   src
   default-language: Haskell2010
diff --git a/src/Mu/Instrumentation/Prometheus.hs b/src/Mu/Instrumentation/Prometheus.hs
--- a/src/Mu/Instrumentation/Prometheus.hs
+++ b/src/Mu/Instrumentation/Prometheus.hs
@@ -49,17 +49,23 @@
 prometheusMetrics metrics NoRpcInfo run = do
   incGauge (activeCalls metrics)
   run `finally` decGauge (activeCalls metrics)
-prometheusMetrics metrics (RpcInfo _pkg (Service sname _) (Method mname _ _) _ _) run = do
+prometheusMetrics metrics (RpcInfo _pkg ss mm _ _) run = do
+  let sname' = case ss of
+                 Service sname _ -> sname
+                 OneOf   sname _ -> sname
+      mname' = case mm of
+                 Just (Method mname _ _) -> mname
+                 Nothing                 -> "<noname>"
   incGauge (activeCalls metrics)
-  withLabel (messagesReceived metrics) (sname, mname) incCounter
+  withLabel (messagesReceived metrics) (sname', mname') incCounter
   ( do -- We are forced to use a MVar because 'withLabel' only allows IO ()
        r <- liftBaseWith $ \runInIO -> do
          result :: MVar (StM m a) <- newEmptyMVar
-         withLabel (callsTotal metrics) (sname, mname) $ \h ->
+         withLabel (callsTotal metrics) (sname', mname') $ \h ->
            h `observeDuration` (runInIO run >>= putMVar result)
          takeMVar result
        x <- restoreM r
-       withLabel (messagesSent metrics) (sname, mname) incCounter
+       withLabel (messagesSent metrics) (sname', mname') incCounter
        pure x )
   `finally` decGauge (activeCalls metrics)