diff --git a/libguile/chars.h b/libguile/chars.h
index 4d1be1db9..e016cb28e 100644
--- a/libguile/chars.h
+++ b/libguile/chars.h
@@ -33,9 +33,9 @@
 #define SCM_CHAR(x) ((scm_t_wchar)SCM_ITAG8_DATA(x))
 
 #define SCM_MAKE_CHAR(x)                                              \
-  (x < 0                                                              \
-   ? SCM_MAKE_ITAG8 ((scm_t_bits) (unsigned char) x, scm_tc8_char)    \
-   : SCM_MAKE_ITAG8 ((scm_t_bits) x, scm_tc8_char))
+  ((x) < 0                                                            \
+   ? SCM_MAKE_ITAG8 ((scm_t_bits) (unsigned char) (x), scm_tc8_char)  \
+   : SCM_MAKE_ITAG8 ((scm_t_bits) (x), scm_tc8_char))
 
 #define SCM_CODEPOINT_MAX (0x10ffff)
 #define SCM_IS_UNICODE_CHAR(c)                                          \