diff --git a/happly.h b/happly.h
index 4ee8c71..83eab2a 100644
--- a/happly.h
+++ b/happly.h
@@ -50,6 +50,7 @@ SOFTWARE.
 
 #include <array>
 #include <cctype>
+#include <cstdint>
 #include <fstream>
 #include <iostream>
 #include <limits>