diff --git a/global-conf.sh b/global-conf.sh
index 43f61e8eac8cb393d613787efaf7e002d5b26224..4f45bd4539e20939d736ba28d4ef6331e6aec243 100644
--- a/global-conf.sh
+++ b/global-conf.sh
@@ -109,6 +109,12 @@ HA_LB1_IP='192.168.41.177'
 HA_LB2=
 HA_LB2_IP=
 
+# -- Tester config --
+# separate values with commas
+TESTER_MS_INSTANCES=
+# TESTER_MAX_INSTANCES is ignored if TESTER_MS_INSTANCES is set
+TESTER_MAX_INSTANCES=
+
 
 # Upstream configuration override
 # -------------------------------
diff --git a/tester.py b/tester.py
index 0ae89ed4fb7a8c71607558be1626f0c285f87233..aab1d99c44e33df4406c669e85b1b5e5659e4db6 100755
--- a/tester.py
+++ b/tester.py
@@ -49,7 +49,6 @@ class Tester():
     VALID_ARGS = ['-e', '-f', '-b', '-d', '-h']
     MAX_LOG_FILES = 50
     NO_MAIL_FAILURES_COUNT = 30
-    MAX_INSTANCES = 2
 
     def __init__(self, *args):
         log('\033[96m-------------------------------\033[0m')
@@ -148,8 +147,28 @@ class Tester():
                 ms_users.append(user)
         # Get MediaServer tests
         if ms_users:
-            if len(ms_users) > self.MAX_INSTANCES:
-                ms_users = ms_users[:self.MAX_INSTANCES]
+            ms_users.sort()
+            cleaned_list = list()
+            instances_to_test = utils.get_conf('TESTER_MS_INSTANCES', '').split(',')
+            if instances_to_test:
+                for val in instances_to_test:
+                    val = val.strip()
+                    if not val:
+                        continue
+                    if val in ms_users:
+                        cleaned_list.append(val)
+                    else:
+                        log('An inexisting instance has been requested for tests: "%s".' % val)
+            if cleaned_list:
+                ms_users = cleaned_list
+            else:
+                try:
+                    max_instances = int(utils.get_conf('TESTER_MAX_INSTANCES') or 2)
+                except Exception as e:
+                    log('TESTER_MAX_INSTANCES has an invalid value: %s' % e)
+                    max_instances = 2
+                if len(ms_users) > max_instances:
+                    ms_users = ms_users[:max_instances]
             # Clone testing suite
             ms_path = os.path.join(path, 'ms-testing-suite')
             if os.path.exists(ms_path):