diff --git a/src/hb-ot-layout.cc b/src/hb-ot-layout.cc
index 1ee23f0ce..e8091ec3e 100644
--- a/src/hb-ot-layout.cc
+++ b/src/hb-ot-layout.cc
@@ -1913,7 +1913,7 @@ inline void hb_ot_map_t::apply (const Proxy &proxy,
       auto &lookup = lookups[table_index][i];
 
       unsigned int lookup_index = lookup.index;
-      if (!buffer->message (font, "start lookup %d feature %c%c%c%c", lookup_index, HB_UNTAG (lookup.feature_tag))) continue;
+      if (!buffer->message (font, "start lookup %d feature '%c%c%c%c'", lookup_index, HB_UNTAG (lookup.feature_tag))) continue;
 
       /* c.digest is a digest of all the current glyphs in the buffer
        * (plus some past glyphs).
@@ -1933,9 +1933,9 @@ inline void hb_ot_map_t::apply (const Proxy &proxy,
 			     proxy.accels[lookup_index]);
       }
       else
-	(void) buffer->message (font, "skipped lookup %d feature %c%c%c%c because no glyph matches", lookup_index, HB_UNTAG (lookup.feature_tag));
+	(void) buffer->message (font, "skipped lookup %d feature '%c%c%c%c' because no glyph matches", lookup_index, HB_UNTAG (lookup.feature_tag));
 
-      (void) buffer->message (font, "end lookup %d feature %c%c%c%c", lookup_index, HB_UNTAG (lookup.feature_tag));
+      (void) buffer->message (font, "end lookup %d feature '%c%c%c%c'", lookup_index, HB_UNTAG (lookup.feature_tag));
     }
 
     if (stage->pause_func)
diff --git a/src/hb-ot-map.hh b/src/hb-ot-map.hh
index 5122c4e56..31a44c766 100644
--- a/src/hb-ot-map.hh
+++ b/src/hb-ot-map.hh
@@ -243,7 +243,7 @@ struct hb_ot_map_builder_t
 				bool          auto_zwj = true,
 				bool          random = false,
 				bool          per_syllable = false,
-				hb_tag_t      feature_tag = HB_TAG_NONE);
+				hb_tag_t      feature_tag = HB_TAG(' ',' ',' ',' '));
 
   struct feature_info_t {
     hb_tag_t tag;