diff --git a/cpp/test_support/test_support.h b/cpp/test_support/test_support.h
index f571ab1..c4050d4 100644
--- a/cpp/test_support/test_support.h
+++ b/cpp/test_support/test_support.h
@@ -8,6 +8,8 @@
 #ifndef MOJO_PUBLIC_CPP_TEST_SUPPORT_TEST_SUPPORT_H_
 #define MOJO_PUBLIC_CPP_TEST_SUPPORT_TEST_SUPPORT_H_
 
+#include <stdio.h>
+
 #include <string>
 #include <vector>