diff --git a/ctype.c b/ctype.c
index 935327164b..faeaf34e67 100644
--- a/ctype.c
+++ b/ctype.c
@@ -14,7 +14,7 @@ enum {
 	P = GIT_PATHSPEC_MAGIC  /* other non-alnum, except for ] and } */
 };
 
-unsigned char sane_ctype[256] = {
+const unsigned char sane_ctype[256] = {
 	0, 0, 0, 0, 0, 0, 0, 0, 0, S, S, 0, 0, S, 0, 0,		/*   0.. 15 */
 	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,		/*  16.. 31 */
 	S, P, P, P, R, P, P, P, R, R, G, R, P, P, R, P,		/*  32.. 47 */
diff --git a/git-compat-util.h b/git-compat-util.h
index 5bd9ad7d2a..80767ff3a1 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -470,7 +470,7 @@ extern const char tolower_trans_tbl[256];
 #undef isupper
 #undef tolower
 #undef toupper
-extern unsigned char sane_ctype[256];
+extern const unsigned char sane_ctype[256];
 #define GIT_SPACE 0x01
 #define GIT_DIGIT 0x02
 #define GIT_ALPHA 0x04