diff --git a/app/build.gradle.kts b/app/build.gradle.kts
index 77ff1e62..917ecbdc 100644
--- a/app/build.gradle.kts
+++ b/app/build.gradle.kts
@@ -218,6 +218,9 @@ dependencies {
     testImplementation("junit:junit:4.13.2")
     testImplementation("org.jetbrains.kotlinx:kotlinx-coroutines-test:1.9.0")
     testImplementation("io.mockk:mockk:1.13.14")
+    // Real org.json on the JVM test classpath so codec round-trips run (Android's stubbed JSONObject
+    // returns defaults under unitTests.isReturnDefaultValues).
+    testImplementation("org.json:json:20240303")
 
     // Canonical-vector capture harness (paired-CI for iOS↔Android E2EE fixture fill)
     androidTestImplementation("androidx.test.ext:junit:1.1.5")