diff --git a/app/models.py b/app/models.py
index e42df9f30c73828f3dac8a24c870c5add9bc2f26..2a6475992651d3d60011294558f1371ff8d0b7b6 100644
--- a/app/models.py
+++ b/app/models.py
@@ -325,7 +325,6 @@ class Network(db.Model):
     address = db.Column(postgresql.CIDR, nullable=False, unique=True)
     first_ip = db.Column(postgresql.INET, nullable=False, unique=True)
     last_ip = db.Column(postgresql.INET, nullable=False, unique=True)
-    gateway = db.Column(postgresql.INET)
     description = db.Column(db.Text)
     admin_only = db.Column(db.Boolean, nullable=False, default=False)
     scope_id = db.Column(db.Integer, db.ForeignKey('network_scope.id'), nullable=False)
@@ -380,6 +379,13 @@ class Network(db.Model):
         return [addr for addr in self.ip_range()
                 if addr not in self.used_ips()]
 
+    def gateway(self):
+        """Return the network gateway"""
+        for interface in self.interfaces:
+            if 'gateway' in [tag.name for tag in interface.tags]:
+                return interface
+        return None
+
     @staticmethod
     def ip_in_network(ip, address):
         """Ensure the IP is in the network
@@ -432,7 +438,6 @@ class Network(db.Model):
             'address': self.address,
             'first_ip': self.first_ip,
             'last_ip': self.last_ip,
-            'gateway': self.gateway,
             'vlan_id': self.vlan_id,
             'description': self.description,
             'admin_only': self.admin_only,
diff --git a/app/network/forms.py b/app/network/forms.py
index 443cb883f7f6c4a337c225f469ef119789b4329c..dc750f6e83f4f00f360ad3280be4ce9670162e90 100644
--- a/app/network/forms.py
+++ b/app/network/forms.py
@@ -15,6 +15,17 @@ from wtforms import (SelectField, StringField, TextAreaField,
 from .. import utils, models
 
 
+def validate_tags(form, field):
+    choices = dict(field.choices)
+    for tag_id in field.data:
+        tag_name = choices.get(tag_id)
+        if tag_name == 'gateway':
+            network = models.Network.query.get(form.network_id.data)
+            existing_gateway = network.gateway()
+            if existing_gateway is not None:
+                raise validators.ValidationError(f'A gateway is already defined for network {network}: {existing_gateway}')
+
+
 class NoValidateSelectField(SelectField):
     """SelectField with no choices validation
 
@@ -65,7 +76,8 @@ class HostForm(FlaskForm):
         validators=[validators.InputRequired(), validators.Regexp(models.HOST_NAME_RE)],
         filters=[utils.lowercase_field])
     mac_id = SelectField('MAC', coerce=utils.coerce_to_str_or_none)
-    tags = SelectMultipleField('Tags', coerce=utils.coerce_to_str_or_none)
+    tags = SelectMultipleField('Tags', coerce=utils.coerce_to_str_or_none,
+                               validators=[validate_tags])
 
     def __init__(self, *args, **kwargs):
         super().__init__(*args, **kwargs)