diff --git a/libguile/chars.h b/libguile/chars.h
index 9d23eba8e..75cbe3e16 100644
--- a/libguile/chars.h
+++ b/libguile/chars.h
@@ -51,7 +51,7 @@
  */
 #define SCM_CHARP(x) (SCM_ITAG8(x) == scm_tc8_char)
 #define SCM_CHAR(x) ((unsigned int)SCM_ITAG8_DATA(x))
-#define SCM_MAKE_CHAR(x) SCM_MAKE_ITAG8((scm_t_bits) x, scm_tc8_char)
+#define SCM_MAKE_CHAR(x) SCM_MAKE_ITAG8((scm_t_bits) (unsigned char) (x), scm_tc8_char)