diff --git a/src/fmt_fp.c b/src/fmt_fp.c
index 765690fce..9ee314760 100644
--- a/src/fmt_fp.c
+++ b/src/fmt_fp.c
@@ -1,3 +1,4 @@
+#include <mrbconf.h>
 #ifndef MRB_NO_FLOAT
 #if defined(MRB_NO_STDIO) || defined(_WIN32) || defined(_WIN64)
 /*