diff --git a/lib/importmap/map.rb b/lib/importmap/map.rb
index 6aa4f4d..43f0421 100644
--- a/lib/importmap/map.rb
+++ b/lib/importmap/map.rb
@@ -141,7 +141,17 @@ def expand_directories_into(paths)
     end
 
     def module_name_from(filename, mapping)
-      [ mapping.under, filename.to_s.remove(filename.extname).remove(/\/?index$/).presence ].compact.join("/")
+      # Regex explanation:
+      # (?:\/|^) # Matches either / OR the start of the string
+      # index   # Matches the word index
+      # $       # Matches the end of the string
+      #
+      # Sample matches
+      # index
+      # folder/index
+      index_regex = /(?:\/|^)index$/
+
+      [ mapping.under, filename.to_s.remove(filename.extname).remove(index_regex).presence ].compact.join("/")
     end
 
     def module_path_from(filename, mapping)
diff --git a/test/dummy/app/javascript/controllers/special_index.js b/test/dummy/app/javascript/controllers/special_index.js
new file mode 100644
index 0000000..5b418da
--- /dev/null
+++ b/test/dummy/app/javascript/controllers/special_index.js
@@ -0,0 +1 @@
+console.log("Sorry - no imports here!")
diff --git a/test/dummy/app/javascript/helpers/requests/special_index.js b/test/dummy/app/javascript/helpers/requests/special_index.js
new file mode 100644
index 0000000..0758b5a
--- /dev/null
+++ b/test/dummy/app/javascript/helpers/requests/special_index.js
@@ -0,0 +1 @@
+console.log("Sorry, nothing helpful here")
diff --git a/test/importmap_test.rb b/test/importmap_test.rb
index bf1bd1e..15c2290 100644
--- a/test/importmap_test.rb
+++ b/test/importmap_test.rb
@@ -44,10 +44,18 @@ def setup
     assert_match %r|assets/controllers/index.*\.js|, generate_importmap_json["imports"]["controllers"]
   end
 
+  test "directory pin mounted under matching subdir doesn't map *_index as root" do
+    assert_match %r|assets/controllers/special_index.*\.js|, generate_importmap_json["imports"]["controllers/special_index"]
+  end
+
   test "directory pin mounted under matching subdir maps index as root at second depth" do
     assert_match %r|assets/helpers/requests/index.*\.js|, generate_importmap_json["imports"]["helpers/requests"]
   end
 
+  test "directory pin mounted under matching subdir doesn't map *_index as root at second depth" do
+    assert_match %r|assets/helpers/requests/special_index.*\.js|, generate_importmap_json["imports"]["helpers/requests/special_index"]
+  end
+
   test "directory pin under custom asset path" do
     assert_match %r|assets/spina/controllers/another_controller-.*\.js|, generate_importmap_json["imports"]["controllers/spina/another_controller"]
     assert_match %r|assets/spina/controllers/deeper/again_controller-.*\.js|, generate_importmap_json["imports"]["controllers/spina/deeper/again_controller"]