diff --git a/calculator.py b/calculator.py
index 6b21d6f..8eafa74 100644
--- a/calculator.py
+++ b/calculator.py
@@ -76,7 +76,8 @@ def _match(self, tokens: List[Token], target_rule: str):
                 # Success!
                 return RuleMatch(target_rule, matched), remaining_tokens
 
-        if rules_map.index(target_rule) + 1 < len(rules_map):
-            return self._match(tokens, rules_map.key_at(rules_map.index(target_rule) + 1))
+        idx = rules_map.index(target_rule)
+        if idx + 1 < len(rules_map):
+            return self._match(tokens, rules_map.key_at(idx + 1))
 
         return None, None
diff --git a/common.py b/common.py
index 5928467..722f8bd 100644
--- a/common.py
+++ b/common.py
@@ -98,7 +98,7 @@ def key_at(self, i):
 
 rules_map = ImmutableIndexedDict((
     ('asn', ('IDT EQL add',)),
-    ('add', ('mul ADD add',)),
+    ('add', ('mul ADD add', 'mui ADD add',)),
     ('mui', ('pow mul',)),
     ('mul', ('pow MUL mul',)),
     ('pow', ('opr POW pow',)),
diff --git a/tests.py b/tests.py
index dcf51b6..4843270 100644
--- a/tests.py
+++ b/tests.py
@@ -55,7 +55,7 @@ class MultiplicationTests(unittest.TestCase):
     def runTest(self):
         self.assertEqual(evaluate('1 * 1'), 1.0)
         self.assertEqual(evaluate('2 * 3'), 6.0)
-        # self.assertEqual(evaluate('-2 * -2'), 4.0)
+        self.assertEqual(evaluate('-2 * -2'), 4.0)
         self.assertEqual(evaluate('(2 * 3) (2 * 3)'), 36.0)
 
 
@@ -116,7 +116,9 @@ def runTest(self):
 
             self.assertTrue(sympy.Matrix(evaluate('identity({})'.format(r_dim), False)).equals(sympy.Identity(r_dim)))
 
-            for _ in range(5):
+            for _ in range(1):
+                print(_)
+
                 mat = [[more_zeroes(random.randint(0, 100)) for _ in range(r_dim)] for _ in range(r_dim)]
                 mat_str = '[' + '|'.join([','.join(map(str, line)) for line in mat]) + ']'