diff --git a/support/contract_handler.cpp b/support/contract_handler.cpp
index d53faff..81c932d 100644
--- a/support/contract_handler.cpp
+++ b/support/contract_handler.cpp
@@ -1,6 +1,8 @@
 #include <contracts>
+#include <cstdio>
 #include <cstdlib>
 
-void handle_contract_violation(const std::contracts::contract_violation&) {
+[[maybe_unused]] static void handle_contract_violation(const std::contracts::contract_violation& violation) {
+    std::fprintf(stderr, "contract violation: %s\n", violation.comment());
     std::abort();
 }