diff --git a/proto/ei-scanner b/proto/ei-scanner
index af30558..5469934 100755
--- a/proto/ei-scanner
+++ b/proto/ei-scanner
@@ -565,6 +565,11 @@ class ProtocolParser(xml.sax.handler.ContentHandler):
                     f"Missing attribute {e} in element '{element}'",
                     self.location,
                 )
+            if since > self.current_interface.version:
+                raise XmlError.create(
+                    f"Invalid 'since' {since} for '{self.current_interface.name}.{name}'",
+                    self.location,
+                )
 
             try:
                 is_bitfield = {
@@ -618,6 +623,12 @@ class ProtocolParser(xml.sax.handler.ContentHandler):
                     f"Missing attribute {e} in element '{element}'",
                     self.location,
                 )
+            if since > self.current_interface.version:
+                raise XmlError.create(
+                    f"Invalid 'since' {since} for '{self.current_interface.name}.{name}'",
+                    self.location,
+                )
+
             is_destructor = attrs.get("type", "") == "destructor"
             opcode = len(self.current_interface.requests)
             request = Request.create(
@@ -652,6 +663,11 @@ class ProtocolParser(xml.sax.handler.ContentHandler):
                     f"Missing attribute {e} in element '{element}'",
                     self.location,
                 )
+            if since > self.current_interface.version:
+                raise XmlError.create(
+                    f"Invalid 'since' {since} for '{self.current_interface.name}.{name}'",
+                    self.location,
+                )
 
             is_destructor = attrs.get("type", "") == "destructor"
             opcode = len(self.current_interface.events)