diff --git a/onedns/exception.py b/onedns/exception.py
index eac61f0..06b5f16 100644
--- a/onedns/exception.py
+++ b/onedns/exception.py
@@ -36,3 +36,11 @@ class RecordDoesNotExist(OneDnsException):
         self.msg = "Record Does Not Exist: {}".format(key)
         if val is not None:
             self.msg += " -> {}".format(val)
+
+
+class DuplicateVMError(OneDnsException):
+    """
+    Raised when two or more VMs share a name or IP
+    """
+    def __init__(self, vmid, key, val):
+        self.msg = "VM one-{} has a duplicate: {} -> {}".format(vmid, key, val)
diff --git a/onedns/server.py b/onedns/server.py
index e504d92..70defaa 100644
--- a/onedns/server.py
+++ b/onedns/server.py
@@ -31,10 +31,24 @@ class OneDNS(resolver.DynamicResolver):
             entries[nicname] = nic.ip
         return entries
 
+    def _check_for_duplicates(self, vm_id, name, ip, zone=None):
+        z = zone or self.zone
+        try:
+            f = z.get_forward(name)
+            raise exception.DuplicateVMError(vm_id, f, ip)
+        except exception.RecordDoesNotExist:
+            pass
+        try:
+            r = z.get_reverse(ip)
+            raise exception.DuplicateVMError(vm_id, ip, r)
+        except exception.RecordDoesNotExist:
+            pass
+
     def add_vm(self, vm, zone=None):
         dns_entries = self._get_vm_dns_entries(vm)
         log.info("Adding VM {id}: {vm}".format(id=vm.id, vm=vm.name))
         for name, ip in dns_entries.items():
+            self._check_for_duplicates(vm.id, name, ip, zone=zone)
             self.add_host(name, ip, zone=zone)
 
     def remove_vm(self, vm, zone=None):
@@ -54,9 +68,12 @@ class OneDNS(resolver.DynamicResolver):
     def sync(self, vms=None):
         z = zone.Zone(self.domain)
         vms = vms or self._one.vms()
+        vms.sort(key=lambda x: x.id)
         for vm in vms:
             try:
                 self.add_vm(vm, zone=z)
             except exception.NoNetworksError as e:
                 e.log(warn=True)
+            except exception.DuplicateVMError as e:
+                e.log(warn=True)
         self.load(z)