diff --git a/tools-webrtc/check_package_boundaries.py b/tools-webrtc/check_package_boundaries.py
index 75588fa7d8..eb791fffb2 100644
--- a/tools-webrtc/check_package_boundaries.py
+++ b/tools-webrtc/check_package_boundaries.py
@@ -54,11 +54,11 @@ class Logger(object):
 def _BuildSubpackagesPattern(packages, query):
   """Returns a regular expression that matches source files inside subpackages
   of the given query."""
-  query += '/'
+  query += os.path.sep
   length = len(query)
   pattern = r'(?P<line_number>\d+)\$\s*"(?P<source_file>(?P<subpackage>'
-  pattern += '|'.join(package[length:] for package in packages
-                      if package.startswith(query))
+  pattern += '|'.join(package[length:].replace(os.path.sep, '/')
+                      for package in packages if package.startswith(query))
   pattern += r')/[\w\./]*)"'
   return re.compile(pattern)
 
diff --git a/tools-webrtc/check_package_boundaries_test.py b/tools-webrtc/check_package_boundaries_test.py
index 437f6e6eac..c59c4850b3 100755
--- a/tools-webrtc/check_package_boundaries_test.py
+++ b/tools-webrtc/check_package_boundaries_test.py
@@ -33,6 +33,7 @@ class Logger(object):
   def log(self, build_file_path, line_number, target_name, source_file,
           subpackage):
     build_file_path = os.path.relpath(build_file_path, self.test_dir)
+    build_file_path = build_file_path.replace(os.path.sep, '/')
     self.messages.append([build_file_path, line_number, target_name,
                           source_file, subpackage])