1 files changed, 2 insertions, 1 deletions

diff --git a/src/charset.h b/src/charset.h
index 58e8f3dfb9d..2b58f88f840 100644
--- a/src/charset.h
+++ b/src/charset.h
@@ -826,7 +826,8 @@ extern Lisp_Object Vauto_fill_chars;
 #define BCOPY_SHORT(from, to, len)              \
   do {                                          \
     int i = len;                                \
-    unsigned char *from_p = from, *to_p = to;   \
+    const unsigned char *from_p = from;         \
+    unsigned char *to_p = to;                   \
     while (i--) *to_p++ = *from_p++;            \
   } while (0)