diff --git a/cpp/src/coords.hpp b/cpp/src/coords.hpp
index 88a6787..4a48807 100644
--- a/cpp/src/coords.hpp
+++ b/cpp/src/coords.hpp
@@ -17,7 +17,10 @@ struct Coords {
         return this->y * 8 + this->x;
     }
 
-    static Coords from_index(int idx) {
+    static Coords from_index(int idx, const char* yes = __builtin_FUNCTION()) {
+        // std::cout << yes << std::endl;
+        if (idx < 0 || idx > 63)
+            throw std::invalid_argument("The index is outside the board...");
         return {idx % 8, idx / 8};
     }