diff --git a/support.cc b/support.cc
index c80cb2d..03bd1bb 100644
--- a/support.cc
+++ b/support.cc
@@ -8,7 +8,9 @@
 
 #define __STDC_LIMIT_MACROS
 #define __STDC_CONSTANT_MACROS
+#define __STDC_FORMAT_MACROS
 
+#include <inttypes.h>
 #include <stdio.h>
 #include <stdint.h>
 #include <errno.h>
@@ -79,7 +81,7 @@ uint64_t GetNumber(uint64_t low, uint64_t high, uint64_t def, const string & pro
          cin.getline(line, 255);
          if (!cin.good())
             exit(5);
-         num = sscanf(line, "%lld", &response);
+         num = sscanf(line, "%" PRIu64, &response);
          if (num == 1) { // user provided a response
             if ((response < low) || (response > high))
                cout << "Value out of range\n";