diff --git a/src/x11_unicode.c b/src/x11_unicode.c
index 6b6a13db..7d4c8a06 100644
--- a/src/x11_unicode.c
+++ b/src/x11_unicode.c
@@ -64,7 +64,7 @@
 //****                KeySym to Unicode mapping table                 ****
 //************************************************************************
 
-static struct codepair {
+static const struct codepair {
   unsigned short keysym;
   unsigned short ucs;
 } keysymtab[] = {