diff --git a/ciphers/hill_cipher.cpp b/ciphers/hill_cipher.cpp
index 1fef0f32e..a57935bf6 100644
--- a/ciphers/hill_cipher.cpp
+++ b/ciphers/hill_cipher.cpp
@@ -35,6 +35,7 @@
 
 #include <cassert>
 #include <cmath>
+#include <cstdint>  /// for integral typedefs
 #include <cstring>
 #include <ctime>
 #include <fstream>