diff --git a/src/__tests__/normalize.spec.ts b/src/__tests__/normalize.spec.ts
index 332ebf5..6f2c2e6 100644
--- a/src/__tests__/normalize.spec.ts
+++ b/src/__tests__/normalize.spec.ts
@@ -10,6 +10,18 @@ describe('normalize', () => {
     });
   });
 
+  describe('normalizes capitalization of Windows drive letters', () => {
+    it.each`
+      path                    | result
+      ${'C:\\foo\\bar'}       | ${'c:/foo/bar'}
+      ${'/C:/foo/bar'}        | ${'c:/foo/bar'}
+      ${'file:///C:/foo/bar'} | ${'c:/foo/bar'}
+      ${'file://C:/foo/bar'}  | ${'c:/foo/bar'}
+    `("normalize('$path')", ({ path, result }) => {
+      expect(normalize(path)).toEqual(result);
+    });
+  });
+
   describe('ignores POSIX slashes', () => {
     it.each`
       path        | result
diff --git a/src/__tests__/startsWithWindowsDrive.spec.ts b/src/__tests__/startsWithWindowsDrive.spec.ts
index 5c03cc4..bc2dca1 100644
--- a/src/__tests__/startsWithWindowsDrive.spec.ts
+++ b/src/__tests__/startsWithWindowsDrive.spec.ts
@@ -1,7 +1,7 @@
 import { startsWithWindowsDrive } from '../';
 
 describe('startsWithWindowsDrive', () => {
-  it.each(['c:\\foo\\bar.json', 'c:\\', 'c:/', 'c:/foo/bar.json', 'c:\\', 'Z:\\', 'A:/'])(
+  it.each(['c:\\foo\\bar.json', 'c:\\', 'c:/', 'c:/', '/C:/', '/C:\\', 'c:/foo/bar.json', 'c:\\', 'Z:\\', 'A:/'])(
     'recognizes driver letter in %s',
     filepath => {
       expect(startsWithWindowsDrive(filepath)).toBe(true);
diff --git a/src/grammar.pegjs b/src/grammar.pegjs
index eb9072b..c093859 100644
--- a/src/grammar.pegjs
+++ b/src/grammar.pegjs
@@ -75,20 +75,20 @@ AbsolutePath
 }
 
   Root
-    = PosixRoot
-    / WindowsRoot
+    = WindowsRoot
+    / PosixRoot
 
-    PosixRoot
-      = Sep {
+    WindowsRoot
+      = Sep ? drive:[A-Za-z] ":" Sep {
         return {
-          drive: null
+          drive: drive.toLowerCase() + ':'
         }
       }
 
-    WindowsRoot
-      = drive:[A-Za-z] ":" Sep {
+    PosixRoot
+      = Sep {
         return {
-          drive: drive.toLowerCase() + ':'
+          drive: null
         }
       }