diff --git a/build/build-clang/build-clang.py b/build/build-clang/build-clang.py
index 8b82918c3f3a..117264fa2d41 100755
--- a/build/build-clang/build-clang.py
+++ b/build/build-clang/build-clang.py
@@ -105,7 +105,11 @@ def import_clang_tidy(source_dir, build_clang_tidy_alpha):
                                    'clang-tools-extra/clang-tidy')
     sys.path.append(clang_plugin_path)
     from import_mozilla_checks import do_import
-    do_import(clang_plugin_path, clang_tidy_path, build_clang_tidy_alpha)
+    import_options = {
+      "alpha": build_clang_tidy_alpha,
+      "external": False
+    }
+    do_import(clang_plugin_path, clang_tidy_path, import_options)
 
 
 def build_package(package_build_dir, cmake_args):
diff --git a/build/clang-plugin/import_mozilla_checks.py b/build/clang-plugin/import_mozilla_checks.py
index ddf3a175c0aa..b4a4e002c0a9 100755
--- a/build/clang-plugin/import_mozilla_checks.py
+++ b/build/clang-plugin/import_mozilla_checks.py
@@ -4,7 +4,6 @@
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 import os
-import sys
 import glob
 import shutil
 import errno
@@ -34,13 +33,17 @@ def copy_dir_contents(src, dest):
                 raise Exception('Directory not copied. Error: %s' % e)
 
 
-def write_cmake(module_path, import_alpha):
+def write_cmake(module_path, import_options):
     names = ['  ' + os.path.basename(f) for f in glob.glob("%s/*.cpp" % module_path)]
-    names += ['  ' + os.path.basename(f) for f in glob.glob("%s/external/*.cpp" % module_path)]
-    if import_alpha:
-        alpha_names = ['  ' + os.path.join("alpha", os.path.basename(f))
-                       for f in glob.glob("%s/alpha/*.cpp" % module_path)]
-        names += alpha_names
+
+    if import_options["external"]:
+        names += ['  ' + os.path.join("external", os.path.basename(f))
+                  for f in glob.glob("%s/external/*.cpp" % (module_path))]
+
+    if import_options["alpha"]:
+        names += ['  ' + os.path.join("alpha", os.path.basename(f))
+                  for f in glob.glob("%s/alpha/*.cpp" % (module_path))]
+
     with open(os.path.join(module_path, 'CMakeLists.txt'), 'w') as f:
         f.write("""set(LLVM_LINK_COMPONENTS support)
 
@@ -98,7 +101,7 @@ def generate_thread_allows(mozilla_path, module_path):
         f.write(ThreadAllows.generate_allows({files, names}))
 
 
-def do_import(mozilla_path, clang_tidy_path, import_alpha):
+def do_import(mozilla_path, clang_tidy_path, import_options):
     module = 'mozilla'
     module_path = os.path.join(clang_tidy_path, module)
     try:
@@ -110,7 +113,7 @@ def do_import(mozilla_path, clang_tidy_path, import_alpha):
     copy_dir_contents(mozilla_path, module_path)
     write_third_party_paths(mozilla_path, module_path)
     generate_thread_allows(mozilla_path, module_path)
-    write_cmake(module_path, import_alpha)
+    write_cmake(module_path, import_options)
     add_moz_module(os.path.join(module_path, '..', 'CMakeLists.txt'))
     with open(os.path.join(module_path, '..', 'CMakeLists.txt'), 'a') as f:
         f.write('add_subdirectory(%s)\n' % module)
@@ -126,29 +129,36 @@ static int LLVM_ATTRIBUTE_UNUSED MozillaModuleAnchorDestination =
 
 
 def main():
-    if len(sys.argv) < 3 or len(sys.argv) > 4:
-        print("""\
-Usage: import_mozilla_checks.py <mozilla-clang-plugin-path> <clang-tidy-path> [import_alpha]
-Imports the Mozilla static analysis checks into a clang-tidy source tree.
-If `import_alpha` is specified then in-tree alpha checkers will be also imported.
-""")
+    import argparse
 
-        return
+    parser = argparse.ArgumentParser(
+        usage="import_mozilla_checks.py <mozilla-clang-plugin-path> <clang-tidy-path> [option]",
+        description="Imports the Mozilla static analysis checks into a clang-tidy source tree."
+    )
+    parser.add_argument('mozilla_path',
+                        help="Full path to mozilla-central/build/clang-plugin")
+    parser.add_argument('clang_tidy_path',
+                        help="Full path to llvm-project/clang-tools-extra/clang-tidy")
+    parser.add_argument('--import-alpha',
+                        help="Enable import of in-tree alpha checks",
+                        action="store_true")
+    parser.add_argument('--import-external',
+                        help="Enable import of in-tree external checks",
+                        action="store_true")
+    args = parser.parse_args()
 
-    mozilla_path = sys.argv[1]
-    if not os.path.isdir(mozilla_path):
+    if not os.path.isdir(args.mozilla_path):
         print("Invalid path to mozilla clang plugin")
 
-    clang_tidy_path = sys.argv[2]
-    if not os.path.isdir(mozilla_path):
+    if not os.path.isdir(args.clang_tidy_path):
         print("Invalid path to clang-tidy source directory")
 
-    import_alpha = False
+    import_options = {
+      "alpha": args.import_alpha,
+      "external": args.import_external
+    }
 
-    if len(sys.argv) == 4 and sys.argv[3] == 'import_alpha':
-        import_alpha = True
-
-    do_import(mozilla_path, clang_tidy_path, import_alpha)
+    do_import(args.mozilla_path, args.clang_tidy_path, import_options)
 
 
 if __name__ == '__main__':