diff --git a/src/hb-shape.cc b/src/hb-shape.cc
index efe3bffc3..812cf5919 100644
--- a/src/hb-shape.cc
+++ b/src/hb-shape.cc
@@ -257,18 +257,18 @@ hb_feature_to_string (hb_feature_t *feature,
   {
     s[len++] = '[';
     if (feature->start)
-      len += MAX (0, snprintf (s + len, ARRAY_LENGTH (s) - len, "%d", feature->start));
+      len += MAX (0, snprintf (s + len, ARRAY_LENGTH (s) - len, "%u", feature->start));
     if (feature->end != feature->start + 1) {
       s[len++] = ':';
       if (feature->end != (unsigned int) -1)
-	len += MAX (0, snprintf (s + len, ARRAY_LENGTH (s) - len, "%d", feature->end));
+	len += MAX (0, snprintf (s + len, ARRAY_LENGTH (s) - len, "%u", feature->end));
     }
     s[len++] = ']';
   }
   if (feature->value > 1)
   {
     s[len++] = '=';
-    len += MAX (0, snprintf (s + len, ARRAY_LENGTH (s) - len, "%d", feature->value));
+    len += MAX (0, snprintf (s + len, ARRAY_LENGTH (s) - len, "%u", feature->value));
   }
   assert (len < ARRAY_LENGTH (s));
   len = MIN (len, size - 1);