diff --git a/src/hb-buffer.hh b/src/hb-buffer.hh
index 01ec250c3..08781869f 100644
--- a/src/hb-buffer.hh
+++ b/src/hb-buffer.hh
@@ -210,9 +210,10 @@ struct hb_buffer_t
   HB_INTERNAL void clear_output ();
   HB_INTERNAL void clear_positions ();
 
-  HB_INTERNAL bool replace_glyphs (unsigned int num_in,
-				   unsigned int num_out,
-				   const hb_codepoint_t *glyph_data);
+  HB_INTERNAL HB_NODISCARD
+  bool replace_glyphs (unsigned int num_in,
+		       unsigned int num_out,
+		       const hb_codepoint_t *glyph_data);
 
   bool replace_glyph (hb_codepoint_t glyph_index)
   {
diff --git a/src/hb-ot-shape-complex-hangul.cc b/src/hb-ot-shape-complex-hangul.cc
index 533e928dc..2f1bf5e1a 100644
--- a/src/hb-ot-shape-complex-hangul.cc
+++ b/src/hb-ot-shape-complex-hangul.cc
@@ -231,7 +231,7 @@ preprocess_text_hangul (const hb_ot_shape_plan_t *plan HB_UNUSED,
 	    chars[0] = 0x25CCu;
 	    chars[1] = u;
 	  }
-	  buffer->replace_glyphs (1, 2, chars);
+	  (void) buffer->replace_glyphs (1, 2, chars);
 	}
 	else
 	{
@@ -273,7 +273,7 @@ preprocess_text_hangul (const hb_ot_shape_plan_t *plan HB_UNUSED,
 	  hb_codepoint_t s = SBase + (l - LBase) * NCount + (v - VBase) * TCount + tindex;
 	  if (font->has_glyph (s))
 	  {
-	    buffer->replace_glyphs (t ? 3 : 2, 1, &s);
+	    (void) buffer->replace_glyphs (t ? 3 : 2, 1, &s);
 	    end = start + 1;
 	    continue;
 	  }
@@ -323,9 +323,7 @@ preprocess_text_hangul (const hb_ot_shape_plan_t *plan HB_UNUSED,
 	hb_codepoint_t new_s = s + new_tindex;
 	if (font->has_glyph (new_s))
 	{
-	  buffer->replace_glyphs (2, 1, &new_s);
-	  if (unlikely (!buffer->successful))
-	    break;
+	  (void) buffer->replace_glyphs (2, 1, &new_s);
 	  end = start + 1;
 	  continue;
 	}
@@ -349,7 +347,7 @@ preprocess_text_hangul (const hb_ot_shape_plan_t *plan HB_UNUSED,
 	    (!tindex || font->has_glyph (decomposed[2])))
 	{
 	  unsigned int s_len = tindex ? 3 : 2;
-	  buffer->replace_glyphs (1, s_len, decomposed);
+	  (void) buffer->replace_glyphs (1, s_len, decomposed);
 
 	  /* If we decomposed an LV because of a non-combining T following,
 	   * we want to include this T in the syllable.
diff --git a/src/hb-ot-shape-normalize.cc b/src/hb-ot-shape-normalize.cc
index 1453d2e3b..776e29902 100644
--- a/src/hb-ot-shape-normalize.cc
+++ b/src/hb-ot-shape-normalize.cc
@@ -229,7 +229,7 @@ handle_variation_selector_cluster (const hb_ot_shape_normalize_context_t *c,
       if (font->get_variation_glyph (buffer->cur().codepoint, buffer->cur(+1).codepoint, &buffer->cur().glyph_index()))
       {
 	hb_codepoint_t unicode = buffer->cur().codepoint;
-	buffer->replace_glyphs (2, 1, &unicode);
+	(void) buffer->replace_glyphs (2, 1, &unicode);
       }
       else
       {