diff --git a/briar-desktop/build.gradle.kts b/briar-desktop/build.gradle.kts
index e39bfcac6c2c6cd6d055ab33e6c346dc577d9ade..3359647f3edb34a6d6ec42f1fc519f45512a21ce 100644
--- a/briar-desktop/build.gradle.kts
+++ b/briar-desktop/build.gradle.kts
@@ -72,6 +72,7 @@ tasks.test {
 
 tasks.withType<KotlinCompile> {
     kotlinOptions.jvmTarget = "11"
+    kotlinOptions.freeCompilerArgs += "-opt-in=kotlin.RequiresOptIn"
 }
 
 tasks.withType<org.gradle.jvm.tasks.Jar> {