diff --git a/lib/grpc/client/adapter.ex b/lib/grpc/client/adapter.ex
index 5160d55f6..427bf5e52 100644
--- a/lib/grpc/client/adapter.ex
+++ b/lib/grpc/client/adapter.ex
@@ -14,7 +14,7 @@ defmodule GRPC.Client.Adapter do
 
   @callback disconnect(channel :: Channel.t()) :: {:ok, Channel.t()} | {:error, any()}
 
-  @callback send_request(stream :: Stream.t(), contents :: binary(), opts :: keyword()) ::
+  @callback send_request(stream :: Stream.t(), contents :: iodata(), opts :: keyword()) ::
               Stream.t()
 
   @doc """
@@ -36,7 +36,7 @@ defmodule GRPC.Client.Adapter do
    Opts:
       - :send_end_stream (optional) - ends the request stream
   """
-  @callback send_data(stream :: Stream.t(), message :: binary(), opts :: keyword()) :: Stream.t()
+  @callback send_data(stream :: Stream.t(), message :: iodata(), opts :: keyword()) :: Stream.t()
 
   @doc """
   Similarly to the option sent on `send_data/2` - :send_end_stream -
diff --git a/lib/grpc/codec.ex b/lib/grpc/codec.ex
index b7a15ab82..e052a95eb 100644
--- a/lib/grpc/codec.ex
+++ b/lib/grpc/codec.ex
@@ -5,7 +5,7 @@ defmodule GRPC.Codec do
 
   @doc ~s(Name is identity of the codec, which will be suffix after content-type "application/grpc+" such as "proto".)
   @callback name() :: String.t()
-  @callback encode(any) :: binary
+  @callback encode(any) :: iodata()
   @callback decode(any, module :: atom) :: any
 
   @doc """
diff --git a/lib/grpc/codec/proto.ex b/lib/grpc/codec/proto.ex
index d3de8b166..db89922ff 100644
--- a/lib/grpc/codec/proto.ex
+++ b/lib/grpc/codec/proto.ex
@@ -5,8 +5,8 @@ defmodule GRPC.Codec.Proto do
     "proto"
   end
 
-  def encode(%mod{} = struct) do
-    mod.encode(struct)
+  def encode(struct) do
+    Protobuf.Encoder.encode_to_iodata(struct)
   end
 
   def decode(binary, module) do
diff --git a/lib/grpc/compressor.ex b/lib/grpc/compressor.ex
index ca0b2439a..37abc2e4e 100644
--- a/lib/grpc/compressor.ex
+++ b/lib/grpc/compressor.ex
@@ -1,5 +1,5 @@
 defmodule GRPC.Compressor do
   @callback name() :: String.t()
-  @callback compress(binary) :: binary
+  @callback compress(iodata()) :: binary
   @callback decompress(binary) :: binary
 end