diff --git a/app/.credo.exs b/app/.credo.exs
index 0a5f34a..88f64e3 100644
--- a/app/.credo.exs
+++ b/app/.credo.exs
@@ -41,6 +41,11 @@
       # If you create your own checks, you must specify the source files for
       # them here, so they can be loaded by Credo before running the analysis.
       #
+      # This is the ONLY load path for lib_dev/ checks: the directory is kept out
+      # of elixirc_paths in mix.exs on purpose, so the module is not also loaded
+      # from a compiled .beam (that double load produced
+      # "warning: redefining module Firehose.Checks.NoConnShadowing").
+      #
       requires: ["lib_dev/firehose/checks/"],
       #
       # If you want to enforce a style guide and need a more traditional linting
diff --git a/app/mix.exs b/app/mix.exs
index f4eb3a0..c1bdc1a 100644
--- a/app/mix.exs
+++ b/app/mix.exs
@@ -33,8 +33,15 @@ defmodule Firehose.MixProject do
   end
 
   # Specifies which paths to compile per environment.
-  defp elixirc_paths(:test), do: ["lib", "lib_dev", "test/support"]
-  defp elixirc_paths(:dev), do: ["lib", "lib_dev"]
+  #
+  # `lib_dev/` is deliberately NOT compiled in any environment: it holds
+  # credo-only checks (Firehose.Checks.NoConnShadowing), and credo loads them
+  # itself from source via `requires:` in .credo.exs. Compiling that path as
+  # well gave every run two load paths for the same module, which surfaces as
+  # "warning: redefining module Firehose.Checks.NoConnShadowing" on a warm
+  # `_build/dev`. Keep the single source load: if you add code under lib_dev/
+  # that is NOT a credo check, give it its own compiled path instead.
+  defp elixirc_paths(:test), do: ["lib", "test/support"]
   defp elixirc_paths(_), do: ["lib"]
 
   # Specifies your project dependencies.