diff --git a/src/OT/Layout/GSUB/Ligature.hh b/src/OT/Layout/GSUB/Ligature.hh
index 6caa80e05..cdb35f525 100644
--- a/src/OT/Layout/GSUB/Ligature.hh
+++ b/src/OT/Layout/GSUB/Ligature.hh
@@ -118,7 +118,7 @@ struct Ligature
 	match_positions[i] += delta;
 	if (i)
 	  *p++ = ',';
-	snprintf (p, sizeof(buf), "%u", match_positions[i]);
+	snprintf (p, sizeof(buf) - (p - buf), "%u", match_positions[i]);
 	p += strlen(p);
       }
 
diff --git a/src/OT/Layout/GSUB/Sequence.hh b/src/OT/Layout/GSUB/Sequence.hh
index abf1c643f..e2190078b 100644
--- a/src/OT/Layout/GSUB/Sequence.hh
+++ b/src/OT/Layout/GSUB/Sequence.hh
@@ -117,7 +117,7 @@ struct Sequence
       {
 	if (buf < p)
 	  *p++ = ',';
-	snprintf (p, sizeof(buf), "%u", i);
+	snprintf (p, sizeof(buf) - (p - buf), "%u", i);
 	p += strlen(p);
       }