diff --git a/spec/git-repository-provider-spec.coffee b/spec/git-repository-provider-spec.coffee
index 7d77adc36..59e3f55af 100644
--- a/spec/git-repository-provider-spec.coffee
+++ b/spec/git-repository-provider-spec.coffee
@@ -54,3 +54,27 @@ describe "GitRepositoryProvider", ->
           directory = new Directory dirPath
           provider.repositoryForDirectory(directory).then (result) ->
             expect(result).toBe null
+
+    describe "when specified a Directory without existsSync()", ->
+      directory = null
+      provider = null
+      beforeEach ->
+        provider = new GitRepositoryProvider atom.project
+
+        # An implementation of Directory that does not implement existsSync().
+        subdirectory = {}
+        directory =
+          getSubdirectory: ->
+          isRoot: -> true
+        spyOn(directory, "getSubdirectory").andReturn(subdirectory)
+
+      it "returns null", ->
+        repo = provider.repositoryForDirectorySync(directory)
+        expect(repo).toBe null
+        expect(directory.getSubdirectory).toHaveBeenCalledWith(".git")
+
+      it "returns a Promise that resolves to null for the async implementation", ->
+        waitsForPromise ->
+          provider.repositoryForDirectory(directory).then (repo) ->
+            expect(repo).toBe null
+            expect(directory.getSubdirectory).toHaveBeenCalledWith(".git")
diff --git a/src/git-repository-provider.coffee b/src/git-repository-provider.coffee
index 210197599..850d30f22 100644
--- a/src/git-repository-provider.coffee
+++ b/src/git-repository-provider.coffee
@@ -11,7 +11,7 @@ findGitDirectorySync = (directory) ->
   # can return cached values rather than always returning new objects:
   # getParent(), getFile(), getSubdirectory().
   gitDir = directory.getSubdirectory('.git')
-  if gitDir.existsSync() and isValidGitDirectorySync gitDir
+  if gitDir.existsSync?() and isValidGitDirectorySync gitDir
     gitDir
   else if directory.isRoot()
     return null