diff --git a/mu-grpc-common.cabal b/mu-grpc-common.cabal
--- a/mu-grpc-common.cabal
+++ b/mu-grpc-common.cabal
@@ -1,5 +1,5 @@
 name:          mu-grpc-common
-version:       0.3.0.0
+version:       0.4.0.0
 synopsis:      gRPC for Mu, common modules for client and server
 description:
   Use @mu-grpc-server@ or @mu-grpc-client@ (the common parts).
@@ -25,16 +25,16 @@
     Mu.GRpc.Bridge
 
   build-depends:
-      avro                    >=0.5
+      avro                    >=0.5.1 && <0.6
     , base                    >=4.12  && <5
-    , binary
-    , bytestring
-    , http2-grpc-proto3-wire
-    , http2-grpc-types
-    , mu-avro                 >=0.3.0
-    , mu-protobuf             >=0.3.0
-    , mu-rpc                  >=0.3.0
-    , mu-schema               >=0.3.0
+    , binary                  >=0.8   && <0.9
+    , bytestring              >=0.10  && <0.11
+    , http2-grpc-proto3-wire  >=0.1   && <0.2
+    , http2-grpc-types        >=0.5   && <0.6
+    , mu-avro                 ==0.4.*
+    , mu-protobuf             ==0.4.*
+    , mu-rpc                  ==0.4.*
+    , mu-schema               ==0.3.*
 
   hs-source-dirs:   src
   default-language: Haskell2010
diff --git a/src/Mu/GRpc/Avro.hs b/src/Mu/GRpc/Avro.hs
--- a/src/Mu/GRpc/Avro.hs
+++ b/src/Mu/GRpc/Avro.hs
@@ -66,12 +66,21 @@
   = ViaToAvroTypeRef { unViaToAvroTypeRef :: t }
 
 instance GRPCInput AvroRPC () where
-  encodeInput _ _ () = mempty
+  encodeInput _ c () = encodeEmpty c
   decodeInput _ _ = runGetIncremental $ pure $ Right ()
 
 instance GRPCOutput AvroRPC () where
-  encodeOutput _ _ () = mempty
+  encodeOutput _ c () = encodeEmpty c
   decodeOutput _ _ = runGetIncremental $ pure $ Right ()
+
+encodeEmpty :: Compression -> Builder
+encodeEmpty compression =
+    mconcat [ singleton (if _compressionByteSet compression then 1 else 0)
+            , putWord32be (fromIntegral $ ByteString.length bin)
+            , fromByteString bin
+            ]
+  where
+    bin = _compressionFunction compression ""
 
 instance forall (sch :: Schema') (sty :: Symbol) (i :: Type).
          ( HasAvroSchema (WithSchema sch sty i)