diff --git a/src/mathlib.cpp b/src/mathlib.cpp
index e0988ed..0c7a038 100644
--- a/src/mathlib.cpp
+++ b/src/mathlib.cpp
@@ -2,7 +2,7 @@
 
 namespace mathlib {
     int add(int a, int b) {
-        return a + b;
+        return a - b;  // intentional break for failure test
     }
 
     std::string greet(const std::string& name) {