diff --git a/src/system.h b/src/system.h
index d47b48c..3397ad7 100644
--- a/src/system.h
+++ b/src/system.h
@@ -89,12 +89,13 @@
 #define HAVE_GETRLIMIT
 #endif
 
-/* printf and size_t support */
+/* printf support for size_t and uint64_t */
 #if defined(WIN32)
-/* Windows uses %Iu for size_t */
 #define PRINTF_SIZE_T "%Iu"
+#define PRINTF_UINT64_T "%I64u"
 #else
 #define PRINTF_SIZE_T "%zu"
+#define PRINTF_UINT64_T ("%" PRIu64)
 #endif
 
 #ifdef SSL_SUPPORT
diff --git a/src/util/misc.c b/src/util/misc.c
index ff5dfc6..592c8b7 100644
--- a/src/util/misc.c
+++ b/src/util/misc.c
@@ -315,7 +315,7 @@ const char* uhub_ulltoa(uint64_t val)
 {
 	static char buf[22];
 
-	return snprintf(buf, sizeof(buf), "%"PRIu64, val) < 0 ? NULL : buf;
+	return snprintf(buf, sizeof(buf), PRINTF_UINT64_T, val) < 0 ? NULL : buf;
 }