diff --git a/ctype.c b/ctype.c
index 0bfebb4e7..fc0225ceb 100644
--- a/ctype.c
+++ b/ctype.c
@@ -30,7 +30,7 @@ const unsigned char sane_ctype[256] = {
 };
 
 /* For case-insensitive kwset */
-const char tolower_trans_tbl[256] = {
+const unsigned char tolower_trans_tbl[256] = {
 	0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07,
 	0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f,
 	0x10, 0x11, 0x12, 0x13, 0x14, 0x15, 0x16, 0x17,
diff --git a/git-compat-util.h b/git-compat-util.h
index e6a4159a2..e96bec3a9 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -554,7 +554,7 @@ static inline int has_extension(const char *filename, const char *ext)
 }
 
 /* in ctype.c, for kwset users */
-extern const char tolower_trans_tbl[256];
+extern const unsigned char tolower_trans_tbl[256];
 
 /* Sane ctype - no locale, and works with signed chars */
 #undef isascii
diff --git a/kwset.c b/kwset.c
index a0f49b3ac..e6236a035 100644
--- a/kwset.c
+++ b/kwset.c
@@ -80,13 +80,13 @@ struct kwset
   struct trie *next[NCHAR];	/* Table of children of the root. */
   char *target;			/* Target string if there's only one. */
   int mind2;			/* Used in Boyer-Moore search for one string. */
-  char const *trans;		/* Character translation table. */
+  unsigned char const *trans;  /* Character translation table. */
 };
 
 /* Allocate and initialize a keyword set object, returning an opaque
    pointer to it.  Return NULL if memory is not available. */
 kwset_t
-kwsalloc (char const *trans)
+kwsalloc (unsigned char const *trans)
 {
   struct kwset *kwset;
 
@@ -381,7 +381,7 @@ kwsprep (kwset_t kws)
   register struct kwset *kwset;
   register int i;
   register struct trie *curr;
-  register char const *trans;
+  register unsigned char const *trans;
   unsigned char delta[NCHAR];
 
   kwset = (struct kwset *) kws;
@@ -590,7 +590,7 @@ cwexec (kwset_t kws, char const *text, size_t len, struct kwsmatch *kwsmatch)
   register int d;
   register char const *end, *qlim;
   register struct tree const *tree;
-  register char const *trans;
+  register unsigned char const *trans;
 
   accept = NULL;
 
diff --git a/kwset.h b/kwset.h
index a21b2eadf..61a134f25 100644
--- a/kwset.h
+++ b/kwset.h
@@ -39,7 +39,7 @@ typedef struct kwset_t* kwset_t;
    if enough memory cannot be obtained.  The argument if non-NULL
    specifies a table of character translations to be applied to all
    pattern and search text. */
-extern kwset_t kwsalloc(char const *);
+extern kwset_t kwsalloc(unsigned char const *);
 
 /* Incrementally extend the keyword set to include the given string.
    Return NULL for success, or an error message.  Remember an index