diff --git a/pkg/native_compiler/lib/snapshot/snapshot.dart b/pkg/native_compiler/lib/snapshot/snapshot.dart
index 9d0eb9fcea8..53ea6bee246 100644
--- a/pkg/native_compiler/lib/snapshot/snapshot.dart
+++ b/pkg/native_compiler/lib/snapshot/snapshot.dart
@@ -428,8 +428,9 @@ class WrapperConstant extends ast.AuxiliaryConstant {
   void visitChildren(ast.Visitor v) => throw 'Should not be called.';
 
   @override
-  void toTextInternal(ast_printer.AstPrinter printer) =>
-      throw 'Should not be called.';
+  void toTextInternal(ast_printer.AstPrinter printer) {
+    printer.write('WrapperConstant(${unwrap})');
+  }
 
   @override
   ast.DartType getType(ast_type_environment.StaticTypeContext context) =>
diff --git a/runtime/vm/module_snapshot.cc b/runtime/vm/module_snapshot.cc
index fead63041a3..2ceafd97faa 100644
--- a/runtime/vm/module_snapshot.cc
+++ b/runtime/vm/module_snapshot.cc
@@ -1057,12 +1057,14 @@ class FunctionTypeDeserializationCluster : public DeserializationCluster {
       const intptr_t num_fixed_params = type.num_fixed_parameters();
       type.set_num_implicit_parameters(1);  // Implicit closure parameter.
       if (num_named_params != 0) {
-        type.SetNumOptionalParameters(num_params - num_named_params,
+        ASSERT(num_params - num_named_params == num_fixed_params);
+        type.SetNumOptionalParameters(num_named_params,
                                       /* are_optional_positional=*/false);
       } else if (num_fixed_params != num_params) {
         type.SetNumOptionalParameters(num_params - num_fixed_params,
                                       /* are_optional_positional=*/true);
       }
+      ASSERT(type.NumParameters() == num_params);
       type.SetIsFinalized();
     }
   }