diff --git a/set_app_domain.py b/set_app_domain.py
index 0d87cfb116f5dfedc39938f7ffd1099f42311c47..88570e2ceeea9591b6e89ef6d3dc9650ea6611d2 100755
--- a/set_app_domain.py
+++ b/set_app_domain.py
@@ -13,8 +13,9 @@ from utils import log
 
 
 class SetAppDomain():
-    USAGE = '''%s [-d] [-h] [app] <domain>
+    USAGE = '''%s [-d] [-f] [-h] [app] <domain>
     -d: Debug mode (can be started with non root users).
+    -f: Force mode (to force replacement of configuration even if there are warnings).
     -h: Show this message.
     app: The application for which the new domain should be set.
          Possible values:
@@ -22,8 +23,8 @@ class SetAppDomain():
          It is possible to specify which MS instance should be targetted
          by using this format: ms-<instance name> (for example ms-msuser).
     domain: The new domain.''' % __file__
-    MS_INSTANCE_USER_PATTERN = r'^[a-z0-9\-]+$'
-    NGINX_SERVER_NAME_PATTERN = r'^\s*server_name\s+([\w\-\_\.\ ]+);$'
+    MS_INSTANCE_USER_PATTERN = r'[a-z0-9\-]+'
+    NGINX_SERVER_NAME_PATTERN = r'\s*server_name\s+([\w\-\_\.\ ]+);'
 
     def __init__(self, *args):
         self.display_header()
@@ -40,6 +41,10 @@ class SetAppDomain():
         # Add to python path
         if root_dir not in sys.path:
             sys.path.append(root_dir)
+        # Check if force mode is enabled
+        self.force = '-f' in args
+        if self.force:
+            args.remove('-f')
         # Check that this script is run by root
         self.debug = '-d' in args
         if self.debug:
@@ -88,11 +93,21 @@ class SetAppDomain():
         with open(path, 'r') as fo:
             vhost = fo.read()
         new_vhost = ''
+        changed_lines = 0
         for line in vhost.split('\n'):
             if re.match(self.NGINX_SERVER_NAME_PATTERN, line):
                 new_vhost += re.sub(self.NGINX_SERVER_NAME_PATTERN, line, new_domain) + '\n'
+                changed_lines += 1
             else:
                 new_vhost += line + '\n'
+        if changed_lines != 2:
+            log('Warning the number of server_name occurence changed in Nginx configuration is not the expected number (2) but is %s.' % changed_lines)
+            if not self.force:
+                log('New configuration will be:')
+                log(new_vhost)
+                log('Use -f to force the replacement of the configuration.')
+                sys.exit(1)
+
         new_vhost = new_vhost.strip() + '\n'
         if new_vhost != vhost:
             if self.debug: