diff --git a/coverage/files.py b/coverage/files.py
index 09f09da79..80cb3a047 100644
--- a/coverage/files.py
+++ b/coverage/files.py
@@ -343,6 +343,7 @@ def add(self, pattern, result):
         match an entire tree, and not just its root.
 
         """
+        pattern = pattern.replace("\\", "/")
         pattern_sep = sep(pattern)
 
         if len(pattern) > 1:
diff --git a/coverage/sqldata.py b/coverage/sqldata.py
index 8d2ed73a5..ab7c437bb 100644
--- a/coverage/sqldata.py
+++ b/coverage/sqldata.py
@@ -384,6 +384,7 @@ def _file_id(self, filename, add=False):
         If filename is not in the database yet, add it if `add` is True.
         If `add` is not True, return None.
         """
+        filename = filename.replace("\\", "/")
         if filename not in self._file_map:
             if add:
                 with self._connect() as con:
diff --git a/tests/test_files.py b/tests/test_files.py
index 5588c373d..fa598896e 100644
--- a/tests/test_files.py
+++ b/tests/test_files.py
@@ -428,4 +428,4 @@ class WindowsFileTest(CoverageTest):
     run_in_temp_dir = False
 
     def test_actual_path(self):
-        assert actual_path(r'c:\Windows') == actual_path(r'C:\wINDOWS')
+        assert actual_path(r'c:/Windows') == actual_path(r'C:\wINDOWS')