diff --git a/signal.hpp b/signal.hpp
index a2c94d3..6243dda 100644
--- a/signal.hpp
+++ b/signal.hpp
@@ -2,7 +2,6 @@
 #define SIGNAL_HPP
 
 #include "callable.hpp"
-#include <cstdio>
 #include <vector>
 
 /*! Observer-listener implementation
@@ -34,6 +33,8 @@ template <class... Args> void Signal<Args...>::invoke(Args... args) {
 }
 
 #ifdef DEBUG
+#include <cstdio>
+
 static inline
 void TEST_signals() {
     struct A {inline void f(int val) {