diff --git a/system/setup b/system/setup
index c546a9ff4bc..3f8250fa742 100755
--- a/system/setup
+++ b/system/setup
@@ -1445,6 +1445,16 @@ class LinuxNetwork(Network):
                     if os.path.exists(path):
                         interfaces[device]['all_slaves_active'] = open(path).read() == '1'
 
+            # Check whether a interface is in promiscuous mode
+            if os.path.exists(os.path.join(path,'flags')):
+                promisc_mode = False
+                # The second byte indicates whether the interface is in promiscuous mode.
+                # 1 = promisc
+                # 0 = no promisc
+                data = int(open(os.path.join(path, 'flags')).read().strip(),16)
+                promisc_mode = (data & 0x0100 > 0)
+                interfaces[device]['promisc'] = promisc_mode
+
             def parse_ip_output(output, secondary=False):
                 for line in output.split('\n'):
                     if not line: