diff --git a/lib/credo/priority.ex b/lib/credo/priority.ex
index bc1f0f6d6..856112c1a 100644
--- a/lib/credo/priority.ex
+++ b/lib/credo/priority.ex
@@ -78,7 +78,7 @@ defmodule Credo.Priority do
           |> Enum.slice(0..(length(names) - 2))
           |> Enum.join(".")
 
-        mod_prio = lookup[mod_name]
+        mod_prio = lookup[mod_name] || 0
 
         {scope_name, prio + mod_prio}
       else
diff --git a/test/credo/check/readability/module_doc_test.exs b/test/credo/check/readability/module_doc_test.exs
index 24e360067..e3dd548d5 100644
--- a/test/credo/check/readability/module_doc_test.exs
+++ b/test/credo/check/readability/module_doc_test.exs
@@ -93,4 +93,13 @@ defmodule Credo.Check.Readability.ModuleDocTest do
     |> run_check(@described_check)
     |> assert_issue()
   end
+
+  test "it should report slightly unexpected code" do
+    """
+    defmodule Person, do: def greet(), do: :howdy
+    """
+    |> to_source_file
+    |> run_check(@described_check)
+    |> assert_issue()
+  end
 end