diff --git a/lib/resolveGitRepo.js b/lib/resolveGitRepo.js
index 03d04ed55..79dfff61d 100644
--- a/lib/resolveGitRepo.js
+++ b/lib/resolveGitRepo.js
@@ -26,6 +26,11 @@ const resolveGitConfigDir = async (gitDir) => {
 }
 
 const determineGitDir = (cwd, relativeDir) => {
+  // if relative dir and cwd have different endings normalize it
+  // this happens under windows, where normalize is unable to normalize git's output
+  if (relativeDir && relativeDir.endsWith(path.sep)) {
+    relativeDir = relativeDir.slice(0, -1)
+  }
   if (relativeDir) {
     // the current working dir is inside the git top-level directory
     return normalize(cwd.substring(0, cwd.lastIndexOf(relativeDir)))
@@ -65,3 +70,6 @@ const resolveGitRepo = async (cwd = process.cwd()) => {
 }
 
 module.exports = resolveGitRepo
+
+// exported for test
+module.exports.determineGitDir = determineGitDir
diff --git a/test/resolveGitRepo.spec.js b/test/resolveGitRepo.spec.js
index 46086ab41..e36e44559 100644
--- a/test/resolveGitRepo.spec.js
+++ b/test/resolveGitRepo.spec.js
@@ -1,7 +1,7 @@
 import normalize from 'normalize-path'
 import path from 'path'
 
-import resolveGitRepo from '../lib/resolveGitRepo'
+import resolveGitRepo, { determineGitDir } from '../lib/resolveGitRepo'
 
 /**
  * resolveGitRepo runs execa, so the mock needs to be disabled for these tests
@@ -48,4 +48,27 @@ describe('resolveGitRepo', () => {
     const { gitDir } = await resolveGitRepo({ cwd: '/' }) // assume root is not a git directory
     expect(gitDir).toEqual(null)
   })
+
+  describe('determineGitDir', () => {
+    it('should resolve to current working dir when relative dir is empty', () => {
+      const cwd = process.cwd()
+      const relativeDir = undefined
+      const rootDir = determineGitDir(cwd, relativeDir)
+      expect(rootDir).toEqual(normalize(cwd))
+    })
+
+    it('should resolve to parent dir when relative dir is child', () => {
+      const relativeDir = 'bar'
+      const cwd = process.cwd() + path.sep + 'bar'
+      const rootDir = determineGitDir(cwd, relativeDir)
+      expect(rootDir).toEqual(normalize(process.cwd()))
+    })
+
+    it('should resolve to parent dir when relative dir is child and child has trailing dir separator', () => {
+      const relativeDir = 'bar' + path.sep
+      const cwd = process.cwd() + path.sep + 'bar'
+      const rootDir = determineGitDir(cwd, relativeDir)
+      expect(rootDir).toEqual(normalize(process.cwd()))
+    })
+  })
 })