diff --git a/nipype/utils/filemanip.py b/nipype/utils/filemanip.py
index ca5cd66f07..6d27e56aa0 100644
--- a/nipype/utils/filemanip.py
+++ b/nipype/utils/filemanip.py
@@ -31,6 +31,7 @@
 
 related_filetype_sets = [
     ('.hdr', '.img', '.mat'),
+    ('.nii', '.mat'),
     ('.BRIK', '.HEAD'),
 ]
 
diff --git a/nipype/utils/tests/test_filemanip.py b/nipype/utils/tests/test_filemanip.py
index bf321c5b9c..eba0794e52 100644
--- a/nipype/utils/tests/test_filemanip.py
+++ b/nipype/utils/tests/test_filemanip.py
@@ -324,7 +324,7 @@ def test_json():
         ('/path/test.hdr',  3, ['/path/test.hdr', '/path/test.img', '/path/test.mat']),
         ('/path/test.BRIK', 2, ['/path/test.BRIK', '/path/test.HEAD']),
         ('/path/test.HEAD', 2, ['/path/test.BRIK', '/path/test.HEAD']),
-        ('/path/foo.nii',   1, [])
+        ('/path/foo.nii',   2, ['/path/foo.nii', '/path/foo.mat'])
         ])
 def test_related_files(file, length, expected_files):
     related_files = get_related_files(file)