diff --git a/unittest/error-bridgedomain5.yaml b/unittest/error-bridgedomain5.yaml
index 55cc1ae..0e14375 100644
--- a/unittest/error-bridgedomain5.yaml
+++ b/unittest/error-bridgedomain5.yaml
@@ -15,5 +15,5 @@ bridgedomains:
   bd13:
     description: "Bridge Domain 13, address but no LCP"
     mtu: 3000
-    interfaces: [ GigabitEthernet1/0/0, GigabitEthernet1/0/0 ]
+    interfaces: [ GigabitEthernet1/0/0, GigabitEthernet1/0/1 ]
     addresses: [ 192.0.2.9/29, 2001:db8:1::1/64 ]
diff --git a/unittest/error-bridgedomain6.yaml b/unittest/error-bridgedomain6.yaml
new file mode 100644
index 0000000..3411634
--- /dev/null
+++ b/unittest/error-bridgedomain6.yaml
@@ -0,0 +1,32 @@
+test:
+  description: "An interface can only occur in one bridgedomain, not two or more"
+  errors:
+    expected:
+     - "bridgedomain .* member .* is not unique"
+    count: 2
+---
+interfaces:
+  GigabitEthernet1/0/0:
+    mtu: 3000
+  GigabitEthernet1/0/1:
+    mtu: 3000
+
+  GigabitEthernet2/0/0:
+    mtu: 3000
+    sub-interfaces:
+      1234:
+        description: "BD11 and BD12"
+
+bridgedomains:
+  bd10:
+    description: "Bridge Domain 10 is well formed"
+    mtu: 3000
+    interfaces: [ GigabitEthernet1/0/0, GigabitEthernet1/0/1 ]
+  bd11:
+    description: "Bridge Domain 11 uses Gi2/0/0.1234, but so does Bridge Domain 12"
+    mtu: 1500
+    interfaces: [ GigabitEthernet2/0/0.1234 ]
+  bd12:
+    description: "Bridge Domain 12 uses Gi2/0/0.1234, but so does Bridge Domain 11"
+    mtu: 1500
+    interfaces: [ GigabitEthernet2/0/0.1234 ]
diff --git a/validator/bridgedomain.py b/validator/bridgedomain.py
index 47ddd80..e13d1ec 100644
--- a/validator/bridgedomain.py
+++ b/validator/bridgedomain.py
@@ -67,6 +67,10 @@ def validate_bridgedomains(yaml):
                     result = False
                     continue
 
+                if not interface.is_bridge_interface_unique(yaml, member):
+                    msgs.append("bridgedomain %s member %s is not unique" % (ifname, member))
+                    result = False
+
                 if interface.has_lcp(yaml, member):
                     msgs.append("bridgedomain %s member %s has an LCP" % (ifname, member))
                     result = False
diff --git a/validator/interface.py b/validator/interface.py
index 756dc3c..f1085a1 100644
--- a/validator/interface.py
+++ b/validator/interface.py
@@ -100,8 +100,41 @@ def is_bond_member(yaml, ifname):
             return True
     return False
 
+
+def get_bridge_interfaces(yaml):
+    """ Returns a list of all interfaces that are bridgedomain members """
+
+    ret = []
+    if not 'bridgedomains' in yaml:
+        return ret
+
+    for ifname, iface in yaml['bridgedomains'].items():
+        if 'interfaces' in iface:
+            ret.extend(iface['interfaces'])
+
+    return ret
+
+def is_bridge_interface_unique(yaml, ifname):
+    """ Returns True if this interface is referenced in bridgedomains zero or one times """
+
+    ifs = get_bridge_interfaces(yaml)
+    n = ifs.count(ifname)
+
+    if n == 0 or n == 1:
+        return True
+    return False
+
+
+def is_bridge_interface(yaml, ifname):
+    """ Returns True if this interface is a member of a BridgeDomain """
+
+    if ifname in get_bridge_interfaces(yaml):
+        return True
+    return False
+
+
 def has_lcp(yaml, ifname):
-    """ Returns True if this interface or sub-interface has an LCP"""
+    """ Returns True if this interface or sub-interface has an LCP """
     if not 'interfaces' in yaml:
         return False