diff --git a/fine/src/semantics.rs b/fine/src/semantics.rs
index 1791023f..098f60c6 100644
--- a/fine/src/semantics.rs
+++ b/fine/src/semantics.rs
@@ -481,7 +481,7 @@ impl<'a> Semantics<'a> {
             TreeKind::ExpressionStatement => self.type_of_expression_statement(tree),
             TreeKind::Identifier => self.type_of_identifier(t, tree),
 
-            _ => None,
+            _ => self.internal_compiler_error(Some(t), "asking for a nonsense type"),
         };
 
         // NOTE: These return `None` if they encounter some problem.