diff --git a/Tests/CPP_Bindings/Source/UnitTest_EncryptionUtils.cpp b/Tests/CPP_Bindings/Source/UnitTest_EncryptionUtils.cpp
index 1ac8db3be..b898dbd87 100644
--- a/Tests/CPP_Bindings/Source/UnitTest_EncryptionUtils.cpp
+++ b/Tests/CPP_Bindings/Source/UnitTest_EncryptionUtils.cpp
@@ -288,7 +288,7 @@ void EncryptionCallbacks::keyDecryptClientCallback(
 		|| Lib3MF::eDigestMethod::SHA1 != ar.GetDigestMethod())
 		*status = 0;
 	else if (nullptr == plainBuffer || 0 == plainSize) {
-		*plainNeeded = 32;
+		*plainNeeded = RsaMethods::getSize(context->key);
 		*status = 32;
 	}
 	else {