diff --git a/lib/credo/check.ex b/lib/credo/check.ex
index 292fadf41..3272ad6e1 100644
--- a/lib/credo/check.ex
+++ b/lib/credo/check.ex
@@ -705,6 +705,7 @@ defmodule Credo.Check do
     column = opts[:column]
     severity = opts[:severity] || Severity.default_value()
     trigger = opts[:trigger]
+    message = to_string(opts[:message])
 
     trigger =
       if trigger == Issue.no_trigger() do
@@ -713,12 +714,23 @@ defmodule Credo.Check do
         to_string(trigger)
       end
 
+    message =
+      if String.valid?(message) do
+        message
+      else
+        IO.warn(
+          "#{check_name(check)} creates an Issue with a `:message` containing invalid bytes: #{inspect(message)}"
+        )
+
+        "(see warning) #{inspect(message)}"
+      end
+
     %Issue{
       check: check,
       category: issue_category,
       priority: priority,
       filename: source_file.filename,
-      message: opts[:message],
+      message: message,
       trigger: trigger,
       line_no: line_no,
       column: column,
@@ -764,6 +776,8 @@ defmodule Credo.Check do
     end
   end
 
+  defp check_name(module), do: Credo.Code.Name.full(module)
+
   # Returns the scope for the given line as a tuple consisting of the call to
   # define the scope (`:defmodule`, `:def`, `:defp` or `:defmacro`) and the
   # name of the scope.
diff --git a/lib/credo/plugin.ex b/lib/credo/plugin.ex
index a17e8ead4..1c5bfaf3d 100644
--- a/lib/credo/plugin.ex
+++ b/lib/credo/plugin.ex
@@ -344,7 +344,9 @@ defmodule Credo.Plugin do
         import Credo.Plugin
 
         def init(exec) do
-          register_cli_switch(exec, :kastle, :string, :X, fn(switch_value) ->
+          exec
+          |> register_command("demo", CredoDemoPlugin.DemoCommand)
+          |> register_cli_switch(:kastle, :string, :X, fn(switch_value) ->
             {:castle, String.upcase(switch_value)}
           end)
         end
diff --git a/test/credo/check/readability/string_sigils_test.exs b/test/credo/check/readability/string_sigils_test.exs
index 49c424870..aaab5141c 100644
--- a/test/credo/check/readability/string_sigils_test.exs
+++ b/test/credo/check/readability/string_sigils_test.exs
@@ -170,7 +170,7 @@ defmodule Credo.Check.Readability.StringSigilsTest do
   end
 
   test "doesn't crash on #729" do
-    log =
+    stderr_output =
       capture_io(:stderr, fn ->
         ~S"""
         defmodule CredoInterpolationError do
@@ -187,6 +187,6 @@ defmodule Credo.Check.Readability.StringSigilsTest do
         |> refute_issues()
       end)
 
-    assert log == ""
+    assert stderr_output == ""
   end
 end
diff --git a/test/credo/check_test.exs b/test/credo/check_test.exs
index 6d82ca688..b92f4de10 100644
--- a/test/credo/check_test.exs
+++ b/test/credo/check_test.exs
@@ -1,6 +1,8 @@
 defmodule Credo.CheckTest do
   use Credo.Test.Case
 
+  import ExUnit.CaptureIO
+
   alias Credo.Check
 
   @generated_lines 1000
@@ -91,4 +93,27 @@ defmodule Credo.CheckTest do
       assert issue.severity == 11
     end)
   end
+
+  defmodule IssueInvalidMessageTestCheck do
+    use Credo.Check
+
+    @message <<70, 111, 117, 110, 100, 32, 109, 105, 115, 115, 112, 101, 108, 108, 101, 100, 32,
+               119, 111, 114, 100, 32, 96, 103, 97, 114, 114, 121, 226, 96, 46>>
+
+    def run(%SourceFile{} = source_file, params \\ []) do
+      IssueMeta.for(source_file, params) |> format_issue(message: @message) |> List.wrap()
+    end
+  end
+
+  test "it should handle an invalid message" do
+    stderr_output =
+      capture_io(:stderr, fn ->
+        "# we do not need code, as the check is creating an issue in any case"
+        |> to_source_file
+        |> run_check(IssueInvalidMessageTestCheck)
+      end)
+
+    assert stderr_output != ""
+    assert stderr_output =~ "containing invalid bytes"
+  end
 end