diff --git a/app/main/views/sms.py b/app/main/views/sms.py
index ac5e6cf67..a3492c585 100644
--- a/app/main/views/sms.py
+++ b/app/main/views/sms.py
@@ -116,9 +116,13 @@ def _format_filename(filename):
     return secure_filename(formatted_name)
 
 
+def _open(file):
+    return open(file, 'r')
+
+
 def _build_upload_result(csv_file):
     try:
-        file = open(csv_file, 'r')
+        file = _open(csv_file, 'r')
         pattern = re.compile(r'^\+44\s?\d{4}\s?\d{6}$')
         reader = csv.DictReader(
             file.read().splitlines(),
diff --git a/tests/app/main/views/test_sms.py b/tests/app/main/views/test_sms.py
index afe7f522a..e2d84b701 100644
--- a/tests/app/main/views/test_sms.py
+++ b/tests/app/main/views/test_sms.py
@@ -37,7 +37,7 @@ def test_upload_csvfile_with_invalid_phone_shows_check_page_with_errors(
             user = create_test_user('active')
             client.login(user)
             upload_data = {'file': file_data}
-            with mock.patch('app.main.views.sms.open', m_open):
+            with mock.patch('app.main.views.sms._open', m_open):
                 response = client.post('/services/123/sms/send',
                                        data=upload_data,
                                        follow_redirects=True)
@@ -66,7 +66,7 @@ def test_upload_csvfile_with_valid_phone_shows_first3_and_last3_numbers(
             user = create_test_user('active')
             client.login(user)
             upload_data = {'file': file_data}
-            with mock.patch('app.main.views.sms.open', m_open):
+            with mock.patch('app.main.views.sms._open', m_open):
                 response = client.post('/services/123/sms/send',
                                        data=upload_data,
                                        follow_redirects=True)
@@ -103,7 +103,7 @@ def test_upload_csvfile_with_valid_phone_shows_all_if_6_or_less_numbers(
             user = create_test_user('active')
             client.login(user)
             upload_data = {'file': file_data}
-            with mock.patch('app.main.views.sms.open', m_open):
+            with mock.patch('app.main.views.sms._open', m_open):
                 response = client.post('/services/123/sms/send',
                                        data=upload_data,
                                        follow_redirects=True)