diff --git a/smnp/ast/parser.py b/smnp/ast/parser.py
index dbe49b7..ffe5f72 100644
--- a/smnp/ast/parser.py
+++ b/smnp/ast/parser.py
@@ -62,7 +62,7 @@ class Parser:
 
     # oneOf -> a | b | c | ...
     @staticmethod
-    def oneOf(*parsers, exception=None, name="or"):
+    def oneOf(*parsers, assertExpected=None, exception=None, name="or"):
         def combinedParser(input):
             snap = input.snapshot()
             for parser in parsers:
@@ -70,6 +70,10 @@ class Parser:
                 if value.result:
                     return value
 
+            if assertExpected is not None:
+                found = f", found '{input.current().rawValue}'" if input.hasCurrent() else ""
+                raise SyntaxException(f"Expected {assertExpected}{found}", input.currentPos())
+
             if exception is not None:
                 if callable(exception):
                     raise exception(input)