diff --git a/src/quicktype-core/language/JavaScript.ts b/src/quicktype-core/language/JavaScript.ts
index 76ca625c..87bc2ceb 100644
--- a/src/quicktype-core/language/JavaScript.ts
+++ b/src/quicktype-core/language/JavaScript.ts
@@ -242,7 +242,11 @@ export class JavaScriptRenderer extends ConvenienceRenderer {
             this.ensureBlankLine();
 
             this.emitBlock([this.serializerFunctionLine(t, name), " "], "", () => {
-                this.emitLine("return JSON.stringify(uncast(value, ", typeMap, "), null, 2);");
+                if (!this._jsOptions.runtimeTypecheck) {
+                    this.emitLine("return JSON.stringify(value);");
+                } else {
+                    this.emitLine("return JSON.stringify(uncast(value, ", typeMap, "), null, 2);");
+                }
             });
         });
         if (this._jsOptions.runtimeTypecheck) {
diff --git a/test/languages.ts b/test/languages.ts
index 64e34a01..328283a5 100644
--- a/test/languages.ts
+++ b/test/languages.ts
@@ -524,7 +524,11 @@ export const TypeScriptLanguage: Language = {
   skipMiscJSON: false,
   skipSchema: ["keyword-unions.schema"], // can't handle "constructor" property
   rendererOptions: { "explicit-unions": "yes" },
-  quickTestRendererOptions: [{ "nice-property-names": "true" }, { "declare-unions": "true" }],
+  quickTestRendererOptions: [
+    { "runtime-typecheck": "false" },
+    { "nice-property-names": "true" },
+    { "declare-unions": "true" }
+  ],
   sourceFiles: ["src/language/TypeScript.ts"]
 };
 
@@ -545,7 +549,7 @@ export const JavaScriptLanguage: Language = {
   skipMiscJSON: false,
   skipSchema: ["keyword-unions.schema"], // can't handle "constructor" property
   rendererOptions: {},
-  quickTestRendererOptions: [],
+  quickTestRendererOptions: [{ "runtime-typecheck": "false" }],
   sourceFiles: ["src/language/JavaScript.ts"]
 };
 
@@ -567,7 +571,11 @@ export const FlowLanguage: Language = {
     "keyword-unions.schema" // can't handle "constructor" property
   ],
   rendererOptions: { "explicit-unions": "yes" },
-  quickTestRendererOptions: [],
+  quickTestRendererOptions: [
+    { "runtime-typecheck": "false" },
+    { "nice-property-names": "true" },
+    { "declare-unions": "true" }
+  ],
   sourceFiles: ["src/language/Flow.ts"]
 };