diff --git a/src/config/network.rs b/src/config/network.rs
index 2545810d..15322a8a 100644
--- a/src/config/network.rs
+++ b/src/config/network.rs
@@ -92,6 +92,15 @@ impl Interface {
         Ok(())
     }
 
+    fn set_interface_type(&mut self, interface_type: NetworkInterfaceType) -> Result<(), Error> {
+        if self.interface_type == NetworkInterfaceType::Unknown {
+            self.interface_type = interface_type;
+        } else if self.interface_type != interface_type {
+            bail!("interface type already defined - cannot change from {:?} to {:?}", self.interface_type, interface_type);
+        }
+        Ok(())
+    }
+
     fn push_addon_option(&mut self, text: String) {
         if self.method_v4.is_none() && self.method_v6.is_some() {
             self.options_v6.push(text);
diff --git a/src/config/network/parser.rs b/src/config/network/parser.rs
index d2595feb..82446517 100644
--- a/src/config/network/parser.rs
+++ b/src/config/network/parser.rs
@@ -174,6 +174,7 @@ impl <R: BufRead> NetworkParser<R> {
 
         Ok(list)
     }
+
     fn parse_iface_attributes(&mut self, interface: &mut Interface) -> Result<(), Error> {
 
         loop {
@@ -194,13 +195,13 @@ impl <R: BufRead> NetworkParser<R> {
                     self.eat(Token::BridgePorts)?;
                     let ports = self.parse_iface_list()?;
                     interface.bridge_ports = Some(ports);
-                    interface.interface_type = NetworkInterfaceType::Bridge;
+                    interface.set_interface_type(NetworkInterfaceType::Bridge)?;
                 }
                 Token::BondSlaves => {
                     self.eat(Token::BondSlaves)?;
                     let slaves = self.parse_iface_list()?;
                     interface.bond_slaves = Some(slaves);
-                    interface.interface_type = NetworkInterfaceType::Bond;
+                    interface.set_interface_type(NetworkInterfaceType::Bond)?;
                 }
                 Token::Netmask => bail!("netmask is deprecated and no longer supported"),
                 _ => {