diff --git a/evm/vm/code_stream.py b/evm/vm/code_stream.py
index f98eaffc12..a6703da38f 100644
--- a/evm/vm/code_stream.py
+++ b/evm/vm/code_stream.py
@@ -10,13 +10,15 @@
 
 class CodeStream(object):
     stream = None
+    depth_processed = None
 
     logger = logging.getLogger('evm.vm.CodeStream')
 
     def __init__(self, code_bytes):
         validate_is_bytes(code_bytes)
         self.stream = io.BytesIO(code_bytes)
-        self._validity_cache = {}
+        self.invalid_positions = set()
+        self.depth_processed = 0
 
     def read(self, size):
         return self.stream.read(size)
@@ -30,6 +32,9 @@ def __iter__(self):
     def __next__(self):
         return self.next()
 
+    def __getitem__(self, i):
+        return self.stream.getvalue()[i]
+
     def next(self):
         next_opcode_as_byte = self.read(1)
 
@@ -63,31 +68,30 @@ def seek(self, pc):
         finally:
             self.pc = anchor_pc
 
-    _validity_cache = None
+    invalid_positions = None
 
     def is_valid_opcode(self, position):
         if position >= len(self):
             return False
-
-        if position not in self._validity_cache:
-            with self.seek(max(0, position - 32)):
-                prefix = self.read(min(position, 32))
-
-            for offset, opcode in enumerate(reversed(prefix)):
-                if opcode < opcode_values.PUSH1 or opcode > opcode_values.PUSH32:
-                    continue
-
-                push_size = 1 + opcode - opcode_values.PUSH1
-                if push_size <= offset:
-                    continue
-
-                opcode_position = position - 1 - offset
-                if not self.is_valid_opcode(opcode_position):
-                    continue
-
-                self._validity_cache[position] = False
-                break
+        if position in self.invalid_positions:
+            return False
+        if position <= self.depth_processed:
+            return True
+        else:
+            i = self.depth_processed
+            while i <= position:
+                opcode = self.__getitem__(i)
+                if opcode >= opcode_values.PUSH1 and opcode <= opcode_values.PUSH32:
+                    left_bound = (i + 1)
+                    right_bound = left_bound + (opcode - 95)
+                    invalid_range = range(left_bound, right_bound)
+                    self.invalid_positions.update(invalid_range)
+                    i = right_bound
+                else:
+                    self.depth_processed = i
+                    i += 1
+
+            if position in self.invalid_positions:
+                return False
             else:
-                self._validity_cache[position] = True
-
-        return self._validity_cache[position]
+                return True
diff --git a/tests/core/code-stream/test_code_stream.py b/tests/core/code-stream/test_code_stream.py
index efa5889bee..73ee9ba03d 100644
--- a/tests/core/code-stream/test_code_stream.py
+++ b/tests/core/code-stream/test_code_stream.py
@@ -55,8 +55,65 @@ def test_seek_reverts_to_original_stream_position_when_context_exits():
     assert code_stream.peek() == opcode_values.ADD
 
 
+def test_get_item_returns_correct_opcode():
+    code_stream = CodeStream(b'\x01\x02\x30')
+    assert code_stream.__getitem__(0) == opcode_values.ADD
+    assert code_stream.__getitem__(1) == opcode_values.MUL
+    assert code_stream.__getitem__(2) == opcode_values.ADDRESS
+
+
 def test_is_valid_opcode_invalidates_bytes_after_PUSHXX_opcodes():
-    code_stream = CodeStream(b'\x01\x60\x02')
+    code_stream = CodeStream(b'\x02\x60\x02\x04')
     assert code_stream.is_valid_opcode(0) is True
     assert code_stream.is_valid_opcode(1) is True
     assert code_stream.is_valid_opcode(2) is False
+    assert code_stream.is_valid_opcode(3) is True
+    assert code_stream.is_valid_opcode(4) is False
+
+
+def test_harder_is_valid_opcode():
+    code_stream = CodeStream(b'\x02\x03\x72' + (b'\x04' * 32) + b'\x05')
+    # valid: 0 - 2 :: 22 - 35
+    # invalid: 3-21 (PUSH19) :: 36+ (too long)
+    assert code_stream.is_valid_opcode(0) is True
+    assert code_stream.is_valid_opcode(1) is True
+    assert code_stream.is_valid_opcode(2) is True
+    assert code_stream.is_valid_opcode(3) is False
+    assert code_stream.is_valid_opcode(21) is False
+    assert code_stream.is_valid_opcode(22) is True
+    assert code_stream.is_valid_opcode(35) is True
+    assert code_stream.is_valid_opcode(36) is False
+
+
+def test_even_harder_is_valid_opcode():
+    test = b'\x02\x03\x7d' + (b'\x04' * 32) + b'\x05\x7e' + (b'\x04' * 35) + b'\x01\x61\x01\x01\x01'
+    code_stream = CodeStream(test)
+    # valid: 0 - 2 :: 33 - 36 :: 68 - 73 :: 76
+    # invalid: 3 - 32 (PUSH30) :: 37 - 67 (PUSH31) :: 74, 75 (PUSH2) :: 77+ (too long)
+    assert code_stream.is_valid_opcode(0) is True
+    assert code_stream.is_valid_opcode(1) is True
+    assert code_stream.is_valid_opcode(2) is True
+    assert code_stream.is_valid_opcode(3) is False
+    assert code_stream.is_valid_opcode(32) is False
+    assert code_stream.is_valid_opcode(33) is True
+    assert code_stream.is_valid_opcode(36) is True
+    assert code_stream.is_valid_opcode(37) is False
+    assert code_stream.is_valid_opcode(67) is False
+    assert code_stream.is_valid_opcode(68) is True
+    assert code_stream.is_valid_opcode(71) is True
+    assert code_stream.is_valid_opcode(72) is True
+    assert code_stream.is_valid_opcode(73) is True
+    assert code_stream.is_valid_opcode(74) is False
+    assert code_stream.is_valid_opcode(75) is False
+    assert code_stream.is_valid_opcode(76) is True
+    assert code_stream.is_valid_opcode(77) is False
+
+
+def test_right_number_of_bytes_invalidated_after_pushxx():
+    code_stream = CodeStream(b'\x02\x03\x60\x02\x02')
+    assert code_stream.is_valid_opcode(0) is True
+    assert code_stream.is_valid_opcode(1) is True
+    assert code_stream.is_valid_opcode(2) is True
+    assert code_stream.is_valid_opcode(3) is False
+    assert code_stream.is_valid_opcode(4) is True
+    assert code_stream.is_valid_opcode(5) is False