diff --git a/json_util.c b/json_util.c
index 00cdc30..c7c2325 100644
--- a/json_util.c
+++ b/json_util.c
@@ -39,6 +39,7 @@
 #endif /* HAVE_UNISTD_H */
 
 #ifdef WIN32
+# define strtoll _strtoi64
 # define WIN32_LEAN_AND_MEAN
 # include <windows.h>
 # include <io.h>