diff --git a/checker/checker_test.go b/checker/checker_test.go
index 6e40e2b80..bd735e1d0 100644
--- a/checker/checker_test.go
+++ b/checker/checker_test.go
@@ -2655,7 +2655,10 @@ func BenchmarkCheck(b *testing.B) {
 			if len(errors.GetErrors()) > 0 {
 				b.Fatalf("Unexpected parse errors: %v", errors.ToDisplayString())
 			}
-			reg, err := types.NewRegistry(types.ProtoTypeDefs(&proto2pb.TestAllTypes{}, &proto3pb.TestAllTypes{}))
+			reg, err := types.NewRegistry(
+				types.JSONFieldNames(tc.env.jsonFieldNames),
+				types.ProtoTypeDefs(&proto2pb.TestAllTypes{}, &proto3pb.TestAllTypes{}),
+			)
 			if err != nil {
 				b.Fatalf("types.NewRegistry() failed: %v", err)
 			}
@@ -2672,6 +2675,9 @@ func BenchmarkCheck(b *testing.B) {
 			if len(tc.opts) != 0 {
 				opts = tc.opts
 			}
+			if tc.env.jsonFieldNames {
+				opts = append(opts, JSONFieldNames(true))
+			}
 			env, err := NewEnv(cont, reg, opts...)
 			if err != nil {
 				b.Fatalf("NewEnv(cont, reg) failed: %v", err)
@@ -2691,7 +2697,7 @@ func BenchmarkCheck(b *testing.B) {
 			}
 			b.ResetTimer()
 			for i := 0; i < b.N; i++ {
-				cAst, errors := Check(pAst, src, env)
+				cAst, errors := Check(ast.Copy(pAst), src, env)
 				if len(errors.GetErrors()) > 0 {
 					errorString := errors.ToDisplayString()
 					if tc.err != "" {