diff --git a/src/test/fuzz/rbf.cpp b/src/test/fuzz/rbf.cpp
index a3138629e2..64eceb6017 100644
--- a/src/test/fuzz/rbf.cpp
+++ b/src/test/fuzz/rbf.cpp
@@ -178,5 +178,5 @@ FUZZ_TARGET(package_rbf, .init = initialize_package_rbf)
 
     // If internals report error, wrapper should too
     auto err_tuple{ImprovesFeerateDiagram(pool, direct_conflicts, all_conflicts, replacement_fees, replacement_vsize)};
-    if (!calc_results.has_value()) assert(err_tuple.has_value());
+    if (!calc_results.has_value()) assert(err_tuple.value().first == DiagramCheckError::UNCALCULABLE);
 }