diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index fad94273..f848d60f 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -44,7 +44,7 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - elixir: 1.18.x
+          - elixir: 1.19.x
             otp: 27
 
     steps:
diff --git a/.tool-versions b/.tool-versions
new file mode 100644
index 00000000..c6f8cdff
--- /dev/null
+++ b/.tool-versions
@@ -0,0 +1,2 @@
+elixir 1.19-otp-27
+erlang 27.3.2
diff --git a/lib/commanded/aggregates/aggregate.ex b/lib/commanded/aggregates/aggregate.ex
index 37e7a514..f16057ad 100644
--- a/lib/commanded/aggregates/aggregate.ex
+++ b/lib/commanded/aggregates/aggregate.ex
@@ -361,7 +361,7 @@ defmodule Commanded.Aggregates.Aggregate do
         # be taken. When it finishes, it will set the timeout.
         {:reply, formatted_reply, state}
       else
-        state = %Aggregate{state | lifespan_timeout: lifespan_timeout}
+        state = %{state | lifespan_timeout: lifespan_timeout}
 
         reply_with_lifespan(formatted_reply, state)
       end
diff --git a/lib/commanded/aggregates/aggregate_state_builder.ex b/lib/commanded/aggregates/aggregate_state_builder.ex
index a6f135a3..21634ae3 100644
--- a/lib/commanded/aggregates/aggregate_state_builder.ex
+++ b/lib/commanded/aggregates/aggregate_state_builder.ex
@@ -96,7 +96,7 @@ defmodule Commanded.Aggregates.AggregateStateBuilder do
         %RecordedEvent{data: data, stream_version: stream_version} = event
         %Aggregate{aggregate_module: aggregate_module, aggregate_state: aggregate_state} = state
 
-        state = %Aggregate{
+        state = %{
           state
           | aggregate_version: stream_version,
             aggregate_state: aggregate_module.apply(aggregate_state, data)
diff --git a/mix.exs b/mix.exs
index f95048d4..4aebaf6e 100644
--- a/mix.exs
+++ b/mix.exs
@@ -20,23 +20,24 @@ defmodule Commanded.Mixfile do
       start_permanent: Mix.env() == :prod,
       consolidate_protocols: Mix.env() == :prod,
       dialyzer: dialyzer(),
-      source_url: @source_url,
-      preferred_cli_env: preferred_cli_env()
+      source_url: @source_url
     ]
   end
 
-  def application do
+  def cli do
     [
-      extra_applications: extra_applications(Mix.env()),
-      mod: {Commanded, []}
+      preferred_envs: [
+        setup: :test,
+        reset: :test,
+        "test.all": :test
+      ]
     ]
   end
 
-  defp preferred_cli_env do
+  def application do
     [
-      setup: :test,
-      reset: :test,
-      "test.all": :test
+      extra_applications: extra_applications(Mix.env()),
+      mod: {Commanded, []}
     ]
   end
 
diff --git a/test/aggregates/aggregate_subscription_test.exs b/test/aggregates/aggregate_subscription_test.exs
index 54ea430d..833ace49 100644
--- a/test/aggregates/aggregate_subscription_test.exs
+++ b/test/aggregates/aggregate_subscription_test.exs
@@ -60,12 +60,9 @@ defmodule Commanded.Aggregates.AggregateSubscriptionTest do
       events =
         EventStore.stream_forward(DefaultApp, account_number)
         |> Enum.to_list()
-        |> Enum.map(fn recorded_event ->
+        |> Enum.map(fn %EventStore.RecordedEvent{} = recorded_event ->
           # specify invalid stream version
-          %EventStore.RecordedEvent{
-            recorded_event
-            | stream_version: 999
-          }
+          %{recorded_event | stream_version: 999}
         end)
 
       # send invalid events, should stop the aggregate process
diff --git a/test/event/support/error/error_event_handler.ex b/test/event/support/error/error_event_handler.ex
index 8cc12c0a..7862ce24 100644
--- a/test/event/support/error/error_event_handler.ex
+++ b/test/event/support/error/error_event_handler.ex
@@ -67,7 +67,7 @@ defmodule Commanded.Event.ErrorEventHandler do
   def error(
         {:error, :failed},
         %ErrorEvent{strategy: "retry_failure_context"} = event,
-        failure_context
+        %FailureContext{} = failure_context
       ) do
     %ErrorEvent{delay: delay, reply_to: reply_to} = event
     %FailureContext{context: context} = failure_context
@@ -78,7 +78,7 @@ defmodule Commanded.Event.ErrorEventHandler do
       |> Map.put(:delay, delay)
 
     # Record failure count in context map
-    failure_context = %FailureContext{failure_context | context: context}
+    failure_context = %{failure_context | context: context}
 
     if Map.get(context, :failures) >= 3 do
       # Stop error handler after third failure