diff --git a/satpy/tests/reader_tests/test_vii_base_nc.py b/satpy/tests/reader_tests/test_vii_base_nc.py
index 93974bf1c8..bba68918cb 100644
--- a/satpy/tests/reader_tests/test_vii_base_nc.py
+++ b/satpy/tests/reader_tests/test_vii_base_nc.py
@@ -46,7 +46,7 @@ def setUp(self, pgi_):
         """Set up the test."""
         # Easiest way to test the reader is to create a test netCDF file on the fly
         # uses a UUID to avoid permission conflicts during execution of tests in parallel
-        self.test_file_name = TEST_FILE + str(uuid.uuid1())
+        self.test_file_name = TEST_FILE + str(uuid.uuid1()) + ".nc"
 
         with Dataset(self.test_file_name, 'w') as nc:
             # Add global attributes
diff --git a/satpy/tests/reader_tests/test_vii_l1b_nc.py b/satpy/tests/reader_tests/test_vii_l1b_nc.py
index 6176cd5106..9d3be6eec3 100644
--- a/satpy/tests/reader_tests/test_vii_l1b_nc.py
+++ b/satpy/tests/reader_tests/test_vii_l1b_nc.py
@@ -42,7 +42,7 @@ def setUp(self):
         """Set up the test."""
         # Easiest way to test the reader is to create a test netCDF file on the fly
         # uses a UUID to avoid permission conflicts during execution of tests in parallel
-        self.test_file_name = TEST_FILE + str(uuid.uuid1())
+        self.test_file_name = TEST_FILE + str(uuid.uuid1()) + ".nc"
 
         with Dataset(self.test_file_name, 'w') as nc:
             # Create data group
diff --git a/satpy/tests/reader_tests/test_vii_l2_nc.py b/satpy/tests/reader_tests/test_vii_l2_nc.py
index 1336da2e7e..fc5d616db1 100644
--- a/satpy/tests/reader_tests/test_vii_l2_nc.py
+++ b/satpy/tests/reader_tests/test_vii_l2_nc.py
@@ -41,7 +41,7 @@ def setUp(self):
         """Set up the test."""
         # Easiest way to test the reader is to create a test netCDF file on the fly
         # uses a UUID to avoid permission conflicts during execution of tests in parallel
-        self.test_file_name = TEST_FILE + str(uuid.uuid1())
+        self.test_file_name = TEST_FILE + str(uuid.uuid1()) + ".nc"
 
         with Dataset(self.test_file_name, 'w') as nc:
             # Create data group
diff --git a/satpy/tests/writer_tests/test_cf.py b/satpy/tests/writer_tests/test_cf.py
index 0c8ca03ac7..513efbd069 100644
--- a/satpy/tests/writer_tests/test_cf.py
+++ b/satpy/tests/writer_tests/test_cf.py
@@ -36,13 +36,14 @@
 class TempFile(object):
     """A temporary filename class."""
 
-    def __init__(self):
+    def __init__(self, suffix=".nc"):
         """Initialize."""
         self.filename = None
+        self.suffix = suffix
 
     def __enter__(self):
         """Enter."""
-        self.handle, self.filename = tempfile.mkstemp()
+        self.handle, self.filename = tempfile.mkstemp(suffix=self.suffix)
         os.close(self.handle)
         return self.filename