diff --git a/packages/quicktype-core/src/language/CPlusPlus/CPlusPlusRenderer.ts b/packages/quicktype-core/src/language/CPlusPlus/CPlusPlusRenderer.ts
index ec99e8029b..ecfd6d62a3 100644
--- a/packages/quicktype-core/src/language/CPlusPlus/CPlusPlusRenderer.ts
+++ b/packages/quicktype-core/src/language/CPlusPlus/CPlusPlusRenderer.ts
@@ -1373,6 +1373,11 @@ export class CPlusPlusRenderer extends ConvenienceRenderer {
             ],
             false,
             () => {
+                if (c.getProperties().size === 0) {
+                    this.emitLine("(void)j;");
+                    this.emitLine("(void)x;");
+                }
+
                 this.forEachClassProperty(c, "none", (name, json, p) => {
                     const [, , setterName] = defined(
                         this._gettersAndSettersForPropertyName.get(name),
@@ -1562,6 +1567,10 @@ export class CPlusPlusRenderer extends ConvenienceRenderer {
             false,
             () => {
                 this.emitLine("j = json::object();");
+                if (c.getProperties().size === 0) {
+                    this.emitLine("(void)x;");
+                }
+
                 this.forEachClassProperty(c, "none", (name, json, p) => {
                     const propType = p.type;
                     cppType = this.cppType(
diff --git a/test/languages.ts b/test/languages.ts
index 6bcfd43611..1e7d486a4f 100644
--- a/test/languages.ts
+++ b/test/languages.ts
@@ -688,7 +688,8 @@ export const CPlusPlusLanguage: Language = {
     base: "test/fixtures/cplusplus",
     setupCommand:
         "curl -o json.hpp https://raw.githubusercontent.com/nlohmann/json/87df1d6708915ffbfa26a051ad7562ecc22e5579/src/json.hpp",
-    compileCommand: "g++ -O0 -o quicktype -std=c++17 main.cpp",
+    compileCommand:
+        "g++ -O0 -o quicktype -std=c++17 -Werror=unused-parameter main.cpp",
     runCommand(sample: string) {
         return `./quicktype "${sample}"`;
     },