diff --git a/android-client/app/build.gradle.kts b/android-client/app/build.gradle.kts
index 92f64a8..a670901 100644
--- a/android-client/app/build.gradle.kts
+++ b/android-client/app/build.gradle.kts
@@ -109,7 +109,11 @@ val debugApkExportName = "onlinemsgclient-debug.apk"
 val prepareLocalDebugTrust by tasks.registering {
     val sourceFile = localDebugCaCertSource
 
-    inputs.file(sourceFile).optional()
+    if (sourceFile.exists()) {
+        inputs.file(sourceFile)
+    } else {
+        inputs.property("localDebugCaCertMissing", true)
+    }
     outputs.dir(generatedLocalDebugTrustDir)
 
     doLast {