diff --git a/include/sbi/sbi_types.h b/include/sbi/sbi_types.h
index 2637faf7..b8a7e6cb 100644
--- a/include/sbi/sbi_types.h
+++ b/include/sbi/sbi_types.h
@@ -14,7 +14,7 @@
 
 /* clang-format off */
 
-typedef char			s8;
+typedef signed char		s8;
 typedef unsigned char		u8;
 typedef unsigned char		uint8_t;