diff --git a/src/hb-cff-interp-dict-common.hh b/src/hb-cff-interp-dict-common.hh
index e589e9fedde7f64190feb036b08e805ed3e1bd09..acbc8cd830149792eb176f11118248b482fa2177 100644
--- a/src/hb-cff-interp-dict-common.hh
+++ b/src/hb-cff-interp-dict-common.hh
@@ -279,6 +279,9 @@ struct TopDictOpSet : DictOpSet
           return false;
         env.clear_args ();
         break;
+      case OpCode_FontMatrix:
+        env.clear_args ();
+        break;
       default:
         return DictOpSet::process_op (op, env);
     }
diff --git a/src/hb-subset-cff-common.hh b/src/hb-subset-cff-common.hh
index 6f944d306233d2f2282ff2d5f6dadb0aeecf50a9..6c2b2a2d3b42ff2fdb059d20d14492b1499e729f 100644
--- a/src/hb-subset-cff-common.hh
+++ b/src/hb-subset-cff-common.hh
@@ -59,7 +59,7 @@ struct ByteStrBuff : hb_vector_t<char, 1>
         return encode_byte ((v >> 8) + OpCode_TwoByteNegInt0) && encode_byte (v & 0xFF);
       }
     }
-    assert ((v & ~0xFFFF) == 0);
+    assert ((-32768 <= v) && (v <= 32767));
     return encode_byte (OpCode_shortint) &&
            encode_byte ((v >> 8) & 0xFF) &&
            encode_byte (v & 0xFF);