diff --git a/proto/ei-scanner b/proto/ei-scanner
index bb7cdc8..e412a80 100755
--- a/proto/ei-scanner
+++ b/proto/ei-scanner
@@ -108,6 +108,8 @@ class Message:
     arguments: list[Argument] = attr.ib(init=False, factory=list)
 
     def add_argument(self, arg: Argument) -> None:
+        if arg.name in [a.name for a in self.arguments]:
+                raise ValueError(f"Duplicate argument name '{arg.name}'")
         self.arguments.append(arg)
 
     @property
@@ -206,8 +208,11 @@ class Enum:
 
     def add_entry(self, entry: Entry) -> None:
         for e in self.entries:
+            if e.name == entry.name:
+                raise ValueError(f"Duplicate enum name '{entry.name}'")
+
             if e.value == entry.value:
-                raise ValueError(f"Duplicate enum value {entry.value}")
+                raise ValueError(f"Duplicate enum value '{entry.value}'")
 
             if self.is_bitmask:
                 if e.value < 0:
@@ -238,12 +243,18 @@ class Interface:
     mode: str = attr.ib()  # "ei" or "eis"
 
     def add_request(self, request: Request) -> None:
+        if request.name in [r.name for r in self.requests]:
+                raise ValueError(f"Duplicate request name '{request.name}'")
         self.requests.append(request)
 
     def add_event(self, event: Event) -> None:
+        if event.name in [r.name for r in self.events]:
+                raise ValueError(f"Duplicate event name '{event.name}'")
         self.events.append(event)
 
     def add_enum(self, enum: Enum) -> None:
+        if enum.name in [r.name for r in self.enums]:
+                raise ValueError(f"Duplicate enum name '{enum.name}'")
         self.enums.append(enum)
 
     @property
@@ -388,7 +399,10 @@ class Protocol(xml.sax.handler.ContentHandler):
                 interface=self.current_interface,
                 is_destructor=is_destructor,
             )
-            self.current_interface.add_request(request)
+            try:
+                self.current_interface.add_request(request)
+            except ValueError as e:
+                raise XmlError(*self.location, str(e))
             self.current_message = request
         elif element == "event":
             if self.current_interface is None:
@@ -418,7 +432,10 @@ class Protocol(xml.sax.handler.ContentHandler):
                 interface=self.current_interface,
                 is_destructor=is_destructor,
             )
-            self.current_interface.add_event(event)
+            try:
+                self.current_interface.add_event(event)
+            except ValueError as e:
+                raise XmlError(*self.location, str(e))
             self.current_message = event
         elif element == "enum":
             if self.current_interface is None:
@@ -453,7 +470,10 @@ class Protocol(xml.sax.handler.ContentHandler):
                 interface=self.current_interface,
                 is_bitmask=is_bitmask,
             )
-            self.current_interface.add_enum(enum)
+            try:
+                self.current_interface.add_enum(enum)
+            except ValueError as e:
+                raise XmlError(*self.location, str(e))
             self.current_message = enum
         elif element == "arg":
             if self.current_interface is None: