diff --git a/lib/elixir_analyzer/constants.ex b/lib/elixir_analyzer/constants.ex
index 19247b35..5496a545 100644
--- a/lib/elixir_analyzer/constants.ex
+++ b/lib/elixir_analyzer/constants.ex
@@ -76,7 +76,7 @@ defmodule ElixirAnalyzer.Constants do
     captains_log_do_not_use_enum_random: "elixir.captains-log.do_not_use_enum_random",
     captains_log_do_not_use_rand_uniform_real: "elixir.captains-log.do_not_use_rand_uniform_real",
     captains_log_use_rand_uniform: "elixir.captains-log.use_rand_uniform",
-    captains_log_use_io_lib: "elixir.captains-log.use_io_lib",
+    captains_log_use_erlang: "elixir.captains-log.use_erlang",
 
     # Community Garden Comments
     community_garden_use_get_and_update: "elixir.community-garden.use_get_and_update",
diff --git a/lib/elixir_analyzer/test_suite/captains_log.ex b/lib/elixir_analyzer/test_suite/captains_log.ex
index 05a1256e..320203e5 100644
--- a/lib/elixir_analyzer/test_suite/captains_log.ex
+++ b/lib/elixir_analyzer/test_suite/captains_log.ex
@@ -47,6 +47,15 @@ defmodule ElixirAnalyzer.TestSuite.CaptainsLog do
     type :essential
     calling_fn module: CaptainsLog, name: :format_stardate
     called_fn module: :io_lib, name: :_
-    comment Constants.captains_log_use_io_lib()
+    comment Constants.captains_log_use_erlang()
+    suppress_if "format_stardate uses :erlang", :pass
+  end
+
+  assert_call "format_stardate uses :erlang" do
+    type :essential
+    calling_fn module: CaptainsLog, name: :format_stardate
+    called_fn module: :erlang, name: :_
+    comment Constants.captains_log_use_erlang()
+    suppress_if "format_stardate uses :io_lib", :pass
   end
 end
diff --git a/test/elixir_analyzer/test_suite/captains_log_test.exs b/test/elixir_analyzer/test_suite/captains_log_test.exs
index b3b783fd..26c7213e 100644
--- a/test/elixir_analyzer/test_suite/captains_log_test.exs
+++ b/test/elixir_analyzer/test_suite/captains_log_test.exs
@@ -97,14 +97,34 @@ defmodule ElixirAnalyzer.ExerciseTest.CaptainsLogTest do
     end
   end
 
-  test_exercise_analysis "format_stardate uses Float.round",
-    comments_include: [Constants.captains_log_use_io_lib()] do
-    defmodule CaptainsLog do
-      def format_stardate(stardate) do
-        if is_float(stardate) do
-          Float.round(stardate, 1) |> to_string()
-        else
-          raise ArgumentError
+  describe "format_stardate uses :io_lib or :erlang" do
+    test_exercise_analysis "format_stardate uses Float.round",
+      comments_include: [Constants.captains_log_use_erlang()] do
+      defmodule CaptainsLog do
+        def format_stardate(stardate) do
+          if is_float(stardate) do
+            Float.round(stardate, 1) |> to_string()
+          else
+            raise ArgumentError
+          end
+        end
+      end
+    end
+
+    test_exercise_analysis "format_stardate uses :io_lib",
+      comments_exclude: [Constants.captains_log_use_erlang()] do
+      defmodule CaptainsLog do
+        def format_stardate(stardate) do
+          to_string(:io_lib.format("~.1f", [stardate]))
+        end
+      end
+    end
+
+    test_exercise_analysis "format_stardate uses :erlang",
+      comments_exclude: [Constants.captains_log_use_erlang()] do
+      defmodule CaptainsLog do
+        def format_stardate(stardate) do
+          :erlang.float_to_binary(stardate, [{:decimals, 1}])
         end
       end
     end