diff --git a/src/xcb_util.c b/src/xcb_util.c
index 8c2a031..58bd12d 100644
--- a/src/xcb_util.c
+++ b/src/xcb_util.c
@@ -59,6 +59,16 @@ int xcb_popcount(uint32_t mask)
     return ((y + (y >> 3)) & 030707070707) % 077;
 }
 
+int xcb_sumof(uint8_t *list, int len)
+{
+  int i, s = 0;
+  for(i=0; i<len; i++) {
+    s += *list;
+    list++;
+  }
+  return s;
+}
+
 static int _xcb_parse_display(const char *name, char **host, char **protocol,
                       int *displayp, int *screenp)
 {
diff --git a/src/xcbext.h b/src/xcbext.h
index 2e10ba2..eb69538 100644
--- a/src/xcbext.h
+++ b/src/xcbext.h
@@ -86,6 +86,7 @@ int xcb_poll_for_reply(xcb_connection_t *c, unsigned int request, void **reply,
 /* xcb_util.c */
 
 int xcb_popcount(uint32_t mask);
+int xcb_sumof(uint8_t *list, int len);
 
 #ifdef __cplusplus
 }