diff --git a/lib/dataloader.ex b/lib/dataloader.ex
index 4559da0..8a0bbea 100644
--- a/lib/dataloader.ex
+++ b/lib/dataloader.ex
@@ -239,7 +239,14 @@ defmodule Dataloader do
   end
 
   defp get_source(loader, source_name) do
-    loader.sources[source_name] || raise "Source does not exist: #{inspect(source_name)}"
+    loader.sources[source_name] ||
+      raise """
+      Source does not exist: #{inspect(source_name)}
+
+      Registered sources are:
+
+      #{inspect(Enum.map(loader.sources, fn {source, _} -> source end))}
+      """
   end
 
   @doc """
@@ -319,8 +326,6 @@ defmodule Dataloader do
   end
 
   @doc """
-  This function is depreacted in favour of `async_safely/3`
-
   This used to be used by both the `Dataloader` module for running multiple
   source queries concurrently, and the `KV` and `Ecto` sources to actually run
   separate batch fetches (e.g. for `Posts` and `Users` at the same time).
@@ -331,6 +336,7 @@ defmodule Dataloader do
 
   Please use `async_safely/3` instead of this for fetching data from sources
   """
+  @doc deprecated: "Use async_safely/3 instead"
   @spec pmap(list(), fun(), keyword()) :: map()
   def pmap(items, fun, opts \\ []) do
     async_safely(__MODULE__, :run_tasks, [items, fun, opts])
diff --git a/lib/dataloader/ecto.ex b/lib/dataloader/ecto.ex
index 69438cf..b9f511d 100644
--- a/lib/dataloader/ecto.ex
+++ b/lib/dataloader/ecto.ex
@@ -265,7 +265,7 @@ if Code.ensure_loaded?(Ecto) do
     @type t :: %__MODULE__{
             repo: Ecto.Repo.t(),
             query: query_fun,
-            repo_opts: Keyword.t(),
+            repo_opts: repo_opts,
             batches: map,
             results: map,
             default_params: map,
@@ -316,6 +316,14 @@ if Code.ensure_loaded?(Ecto) do
     Default implementation for loading a batch. Handles looking up records by
     column
     """
+    @spec run_batch(
+            repo :: Ecto.Repo.t(),
+            queryable :: Ecto.Queryable.t(),
+            query :: Ecto.Query.t(),
+            col :: any,
+            inputs :: [any],
+            repo_opts :: repo_opts
+          ) :: [any]
     def run_batch(repo, _queryable, query, col, inputs, repo_opts) do
       results = load_rows(col, inputs, query, repo, repo_opts)
       grouped_results = group_results(results, col)
@@ -482,8 +490,12 @@ if Code.ensure_loaded?(Ecto) do
           {:primary, col, value} ->
             {{:queryable, self(), queryable, :one, col, opts}, value, value}
 
-          _ ->
-            raise "cardinality required unless using primary key"
+          {:not_primary, col, _value} ->
+            raise """
+            Cardinality required unless using primary key
+
+            The non-primary key column specified was: #{inspect(col)}
+            """
         end
       end
 
diff --git a/lib/dataloader/kv.ex b/lib/dataloader/kv.ex
index 9b04889..d9940a7 100644
--- a/lib/dataloader/kv.ex
+++ b/lib/dataloader/kv.ex
@@ -80,8 +80,8 @@ defmodule Dataloader.KV do
 
     defp fetched?(results, batch_key, id) do
       case results do
-        %{^batch_key => %{^id => {:error, _}}}  -> false
-        %{^batch_key => %{^id => _}}  -> true
+        %{^batch_key => %{^id => {:error, _}}} -> false
+        %{^batch_key => %{^id => _}} -> true
         _ -> false
       end
     end
diff --git a/test/dataloader/ecto_test.exs b/test/dataloader/ecto_test.exs
index 460561e..9830a98 100644
--- a/test/dataloader/ecto_test.exs
+++ b/test/dataloader/ecto_test.exs
@@ -289,7 +289,7 @@ defmodule Dataloader.EctoTest do
         Dataloader.load(loader, Test, {User, %{foo: :bar}}, username: 1)
       end)
 
-    assert message =~ "cardinality"
+    assert message =~ "Cardinality"
   end
 
   test "works with has many through", %{loader: loader} do
diff --git a/test/dataloader_test.exs b/test/dataloader_test.exs
index 9115231..7ff1f16 100644
--- a/test/dataloader_test.exs
+++ b/test/dataloader_test.exs
@@ -53,6 +53,23 @@ defmodule DataloaderTest do
     end
   end
 
+  describe "unknown sources" do
+    test "load/3 for unknown source returns error", %{loader: loader} do
+      assert_raise RuntimeError, ~r/Source does not exist/, fn ->
+        loader |> Dataloader.load(:bogus, :users, "ben")
+      end
+    end
+
+    test "get/3 for unknown source returns error", %{loader: loader} do
+      assert_raise RuntimeError, ~r/Source does not exist/, fn ->
+        loader
+        |> Dataloader.load(:test, :users, "ben")
+        |> Dataloader.run()
+        |> Dataloader.get(:bogus, :users, "ben")
+      end
+    end
+  end
+
   describe "get methods when configured to raise an error" do
     test "get/4 returns a value when successful", %{loader: loader} do
       result =