diff --git a/lib/kafka_ex/consumer_group/manager.ex b/lib/kafka_ex/consumer_group/manager.ex
index cb41691d..c2810f92 100644
--- a/lib/kafka_ex/consumer_group/manager.ex
+++ b/lib/kafka_ex/consumer_group/manager.ex
@@ -169,7 +169,7 @@ defmodule KafkaEx.ConsumerGroup.Manager do
   # timeout.
   def terminate(_reason, %State{generation_id: nil, member_id: nil}), do: :ok
   def terminate(_reason, %State{} = state) do
-    :ok = leave(state)
+    {:ok, _state} = leave(state)
     Process.unlink(state.worker_name)
     KafkaEx.stop_worker(state.worker_name)
   end
@@ -190,8 +190,6 @@ defmodule KafkaEx.ConsumerGroup.Manager do
   # the leader, which is reponsible for assigning partitions to all of the
   # group members. Once a `JoinGroupResponse` is received, all group members
   # must send a `SyncGroupRequest` (see sync/2).
-
-  @spec join(State.t) :: {:ok, State.t}
   defp join(
     %State{
       worker_name: worker_name,
@@ -253,41 +251,40 @@ defmodule KafkaEx.ConsumerGroup.Manager do
   # Upon receiving a successful `SyncGroupResponse`, a group member is free to
   # start consuming from its assigned partitions, but must send periodic
   # heartbeats to the coordinating broker.
-  @spec sync(State.t, assignments) :: {:ok, State.t}
   defp sync(
-    %State{
-      group_name: group_name,
-      member_id: member_id,
-      generation_id: generation_id,
-      worker_name: worker_name,
-      session_timeout: session_timeout
-    } = state,
-    assignments
-  ) do
+         %State{
+           group_name: group_name,
+           member_id: member_id,
+           generation_id: generation_id,
+           worker_name: worker_name,
+           session_timeout: session_timeout
+         } = state,
+         assignments
+       ) do
     sync_request = %SyncGroupRequest{
       group_name: group_name,
       member_id: member_id,
       generation_id: generation_id,
-      assignments: assignments,
+      assignments: assignments
     }
 
-    sync_group_response = KafkaEx.sync_group(
-      sync_request,
-      worker_name: worker_name,
-      timeout: session_timeout + @session_timeout_padding
-    )
+    %SyncGroupResponse{error_code: error_code, assignments: assignments} =
+      KafkaEx.sync_group(
+        sync_request,
+        worker_name: worker_name,
+        timeout: session_timeout + @session_timeout_padding
+      )
 
-    case sync_group_response do
-      %SyncGroupResponse{error_code: :no_error, assignments: assignments} ->
+    case error_code do
+      :no_error ->
         # On a high-latency connection, the join/sync process takes a long
         # time. Send a heartbeat as soon as possible to avoid hitting the
         # session timeout.
-        new_state = state
-                    |> start_heartbeat_timer()
-                    |> stop_consumer()
-                    |> start_consumer(unpack_assignments(assignments))
-        {:ok, new_state}
-      %SyncGroupResponse{error_code: :rebalance_in_progress} ->
+        {:ok, state} = start_heartbeat_timer(state)
+        {:ok, state} = stop_consumer(state)
+        start_consumer(state, unpack_assignments(assignments))
+
+      :rebalance_in_progress ->
         rebalance(state)
     end
   end
@@ -296,7 +293,6 @@ defmodule KafkaEx.ConsumerGroup.Manager do
   # broker that the member is leaving the group without having to wait for the
   # session timeout to expire. Leaving a group triggers a rebalance for the
   # remaining group members.
-  @spec leave(State.t) :: :ok
   defp leave(
     %State{
       worker_name: worker_name,
@@ -323,19 +319,17 @@ defmodule KafkaEx.ConsumerGroup.Manager do
       end)
     end
 
-    :ok
+    {:ok, state}
   end
 
   # When instructed that a rebalance is in progress, a group member must rejoin
   # the group with `JoinGroupRequest` (see join/1). To keep the state
   # synchronized during the join/sync phase, each member pauses its consumers
   # and commits its offsets before rejoining the group.
-  @spec rebalance(State.t) :: {:ok, State.t}
   defp rebalance(%State{} = state) do
-    state
-    |> stop_heartbeat_timer()
-    |> stop_consumer()
-    |> join()
+    {:ok, state} = stop_heartbeat_timer(state)
+    {:ok, state} = stop_consumer(state)
+    join(state)
   end
 
   ### Timer Management
@@ -343,29 +337,27 @@ defmodule KafkaEx.ConsumerGroup.Manager do
   # Starts a heartbeat process to send heartbeats in the background to keep the
   # consumers active even if it takes a long time to process a batch of
   # messages.
-  @spec start_heartbeat_timer(State.t) :: State.t
   defp start_heartbeat_timer(%State{} = state) do
     {:ok, timer} = Heartbeat.start_link(state)
 
-    %State{state | heartbeat_timer: timer}
+    {:ok, %State{state | heartbeat_timer: timer}}
   end
 
   # Stops the heartbeat process.
-  @spec stop_heartbeat_timer(State.t) :: State.t
-  defp stop_heartbeat_timer(%State{heartbeat_timer: nil} = state), do: state
+  defp stop_heartbeat_timer(%State{heartbeat_timer: nil} = state), do: {:ok, state}
   defp stop_heartbeat_timer(
     %State{heartbeat_timer: heartbeat_timer} = state
   ) do
     if Process.alive?(heartbeat_timer) do
       :gen_server.stop(heartbeat_timer)
     end
-    %State{state | heartbeat_timer: nil}
+    new_state = %State{state | heartbeat_timer: nil}
+    {:ok, new_state}
   end
 
   ### Consumer Management
 
   # Starts consuming from the member's assigned partitions.
-  @spec start_consumer(State.t, assignments) :: State.t
   defp start_consumer(
     %State{
       consumer_module: consumer_module,
@@ -383,19 +375,19 @@ defmodule KafkaEx.ConsumerGroup.Manager do
       consumer_opts
     )
 
-    %{
+    state = %{
       state |
       assignments: assignments,
       consumer_supervisor_pid: consumer_supervisor_pid
     }
+    {:ok, state}
   end
 
   # Stops consuming from the member's assigned partitions and commits offsets.
-  @spec stop_consumer(State.t) :: State.t
   defp stop_consumer(%State{supervisor_pid: pid} = state) do
     :ok = ConsumerGroup.stop_consumer(pid)
 
-    state
+    {:ok, state}
   end
 
   ### Partition Assignment
@@ -404,7 +396,6 @@ defmodule KafkaEx.ConsumerGroup.Manager do
   # interest to this consumer group. This function returns a list of
   # topic/partition tuples that can be passed to a GenConsumer's
   # `assign_partitions` method.
-  @spec assignable_partitions(State.t) :: assignments()
   defp assignable_partitions(
     %State{worker_name: worker_name, topics: topics, group_name: group_name}
   ) do
@@ -434,7 +425,6 @@ defmodule KafkaEx.ConsumerGroup.Manager do
   # of topic/partition tuples, obtained from `assignable_partitions/1`. The
   # return value is a complete list of member assignments in the format needed
   # by `SyncGroupResponse`.
-  @spec assign_partitions(State.t, list(), list()) :: list()
   defp assign_partitions(
     %State{partition_assignment_callback: partition_assignment_callback},
     members,