diff --git a/src/ddsrt/src/xmlparser.c b/src/ddsrt/src/xmlparser.c
index 828d40e..0096c88 100644
--- a/src/ddsrt/src/xmlparser.c
+++ b/src/ddsrt/src/xmlparser.c
@@ -36,7 +36,7 @@ struct ddsrt_xmlp_state {
     size_t cbufmax; /* allocated size of cbuf (cbufn <= cbufmax) */
     size_t cbufmark; /* NORMARKER or marker position (cbufmark <= cbufp) for rewinding */
     int eof; /* fake EOF (for treating missing close tags as EOF) */
-    char *cbuf; /* parser input buffer */
+    unsigned char *cbuf; /* parser input buffer */
     FILE *fp; /* file to refill cbuf from, or NULL if parsing a string */
     int line; /* current line number */
     int prevline; /* line number at last token */
@@ -147,7 +147,7 @@ struct ddsrt_xmlp_state *ddsrt_xmlp_new_string (const char *string, void *varg,
     st = ddsrt_malloc (sizeof (*st));
     st->cbufn = strlen (string);
     st->cbufmax = st->cbufn;
-    st->cbuf = (char *) string;
+    st->cbuf = (unsigned char *) string;
     st->fp = NULL;
     ddsrt_xmlp_new_common (st);
     ddsrt_xmlp_new_setCB (st, varg, cb);
@@ -239,7 +239,7 @@ static void rewind_to_input_marker (struct ddsrt_xmlp_state *st)
 
 static int next_char (struct ddsrt_xmlp_state *st)
 {
-    char c;
+    unsigned char c;
     if (!make_chars_available (st, 1)) {
         return TOK_EOF;
     }