diff --git a/mythril/analysis/modules/integer.py b/mythril/analysis/modules/integer.py
index 9bd354a7..515a0e85 100644
--- a/mythril/analysis/modules/integer.py
+++ b/mythril/analysis/modules/integer.py
@@ -167,33 +167,19 @@ class IntegerOverflowUnderflowModule(DetectionModule):
 
             constraints = copy.deepcopy(node.constraints)
 
-            # Filter for patterns that indicate benign underflows
-
-            # Pattern 1: (96 + calldatasize_MAIN) - (96), where (96 + calldatasize_MAIN) would underflow if calldatasize is very large.
-            # Pattern 2: (256*If(1 & storage_0 == 0, 1, 0)) - 1, this would underlow if storage_0 = 0
             if type(op0) == int and type(op1) == int:
                 return []
-            if re.search(r"calldatasize_", str(op0)):
-                return []
-            if re.search(r"256\*.*If\(1", str(op0), re.DOTALL) or re.search(
-                r"256\*.*If\(1", str(op1), re.DOTALL
-            ):
-                return []
-            if re.search(r"32 \+.*calldata", str(op0), re.DOTALL) or re.search(
-                r"32 \+.*calldata", str(op1), re.DOTALL
-            ):
-                return []
 
             logging.debug(
                 "[INTEGER_UNDERFLOW] Checking SUB {0}, {1} at address {2}".format(
                     str(op0), str(op1), str(instruction["address"])
                 )
             )
+
             allowed_types = [int, BitVecRef, BitVecNumRef]
 
             if type(op0) in allowed_types and type(op1) in allowed_types:
-                constraints.append(UGT(op1, op0))
-
+                constraints.append(Not(BVSubNoUnderflow(op0, op1, signed=False)))
                 try:
 
                     model = solver.get_model(constraints)
diff --git a/mythril/analysis/solver.py b/mythril/analysis/solver.py
index 2848f205..b91cc498 100644
--- a/mythril/analysis/solver.py
+++ b/mythril/analysis/solver.py
@@ -103,7 +103,7 @@ def get_transaction_sequence(global_state, constraints):
         concrete_transactions[tx_id]["calldata"] = "0x" + "".join(
             [
                 hex(b)[2:] if len(hex(b)) % 2 == 0 else "0" + hex(b)[2:]
-                for b in transaction.call_data.concretized(model)
+                for b in transaction.call_data.concrete(model)
             ]
         )
 
diff --git a/mythril/laser/ethereum/call.py b/mythril/laser/ethereum/call.py
index cc567b89..de14d42e 100644
--- a/mythril/laser/ethereum/call.py
+++ b/mythril/laser/ethereum/call.py
@@ -3,7 +3,11 @@ from typing import Union
 from z3 import simplify, ExprRef, Extract
 import mythril.laser.ethereum.util as util
 from mythril.laser.ethereum.state.account import Account
-from mythril.laser.ethereum.state.calldata import CalldataType, Calldata
+from mythril.laser.ethereum.state.calldata import (
+    CalldataType,
+    SymbolicCalldata,
+    ConcreteCalldata,
+)
 from mythril.laser.ethereum.state.global_state import GlobalState
 from mythril.support.loader import DynLoader
 import re
@@ -174,12 +178,12 @@ def get_call_data(
                     starting_calldata.append(Extract(j + 7, j, elem))
                     i += 1
 
-        call_data = Calldata(transaction_id, starting_calldata)
+        call_data = ConcreteCalldata(transaction_id, starting_calldata)
         call_data_type = CalldataType.CONCRETE
         logging.debug("Calldata: " + str(call_data))
     except TypeError:
         logging.debug("Unsupported symbolic calldata offset")
         call_data_type = CalldataType.SYMBOLIC
-        call_data = Calldata("{}_internalcall".format(transaction_id))
+        call_data = SymbolicCalldata("{}_internalcall".format(transaction_id))
 
     return call_data, call_data_type
diff --git a/mythril/laser/ethereum/instructions.py b/mythril/laser/ethereum/instructions.py
index 7ade087d..005244e2 100644
--- a/mythril/laser/ethereum/instructions.py
+++ b/mythril/laser/ethereum/instructions.py
@@ -42,7 +42,7 @@ from mythril.laser.ethereum.evm_exceptions import (
 )
 from mythril.laser.ethereum.gas import OPCODE_GAS
 from mythril.laser.ethereum.keccak import KeccakFunctionManager
-from mythril.laser.ethereum.state.calldata import CalldataType, Calldata
+from mythril.laser.ethereum.state.calldata import CalldataType
 from mythril.laser.ethereum.state.global_state import GlobalState
 from mythril.laser.ethereum.transaction import (
     MessageCallTransaction,
@@ -458,10 +458,9 @@ class Instruction:
         environment = global_state.environment
         op0 = state.stack.pop()
 
-        value, constraints = environment.calldata.get_word_at(op0)
+        value = environment.calldata.get_word_at(op0)
 
         state.stack.append(value)
-        state.constraints.extend(constraints)
 
         return [global_state]
 
@@ -541,9 +540,8 @@ class Instruction:
                 i_data = dstart
                 new_memory = []
                 for i in range(size):
-                    value, constraints = environment.calldata[i_data]
+                    value = environment.calldata[i_data]
                     new_memory.append(value)
-                    state.constraints.extend(constraints)
 
                     i_data = (
                         i_data + 1 if isinstance(i_data, int) else simplify(i_data + 1)
diff --git a/mythril/laser/ethereum/natives.py b/mythril/laser/ethereum/natives.py
index ed8a0c4c..f6293831 100644
--- a/mythril/laser/ethereum/natives.py
+++ b/mythril/laser/ethereum/natives.py
@@ -8,7 +8,7 @@ from ethereum.utils import ecrecover_to_pub
 from py_ecc.secp256k1 import N as secp256k1n
 from rlp.utils import ALL_BYTES
 
-from mythril.laser.ethereum.state.calldata import Calldata
+from mythril.laser.ethereum.state.calldata import BaseCalldata
 from mythril.laser.ethereum.util import bytearray_to_int, sha3, get_concrete_int
 from z3 import Concat, simplify
 
@@ -88,7 +88,7 @@ def identity(data: Union[bytes, str, List[int]]) -> bytes:
     return result
 
 
-def native_contracts(address: int, data: Calldata):
+def native_contracts(address: int, data: BaseCalldata):
     """
     takes integer address 1, 2, 3, 4
     """
diff --git a/mythril/laser/ethereum/state/calldata.py b/mythril/laser/ethereum/state/calldata.py
index 1fd83316..3cbbf834 100644
--- a/mythril/laser/ethereum/state/calldata.py
+++ b/mythril/laser/ethereum/state/calldata.py
@@ -1,17 +1,7 @@
 from enum import Enum
 from typing import Union, Any
-from z3 import (
-    BitVecVal,
-    BitVecRef,
-    BitVecSort,
-    BitVec,
-    Implies,
-    simplify,
-    Concat,
-    UGT,
-    Array,
-)
-from z3.z3types import Z3Exception
+from z3 import BitVecVal, BitVecRef, BitVec, simplify, Concat, If, ExprRef
+from z3.z3types import Z3Exception, Model
 
 from mythril.laser.ethereum.util import get_concrete_int
 
@@ -21,84 +11,133 @@ class CalldataType(Enum):
     SYMBOLIC = 2
 
 
-class Calldata:
+class BaseCalldata:
     """
-    Calldata class representing the calldata of a transaction
+    Base calldata class
+    This represents the calldata provided when sending a transaction to a contract
     """
 
-    def __init__(self, tx_id, starting_calldata=None):
-        """
-        Constructor for Calldata
-        :param tx_id: unique value representing the transaction the calldata is for
-        :param starting_calldata: byte array representing the concrete calldata of a transaction
-        """
+    def __init__(self, tx_id):
         self.tx_id = tx_id
-        if starting_calldata is not None:
-            self._calldata = []
-            self.calldatasize = BitVecVal(len(starting_calldata), 256)
-            self.concrete = True
-        else:
-            self._calldata = Array(
-                "{}_calldata".format(self.tx_id), BitVecSort(256), BitVecSort(8)
-            )
-            self.calldatasize = BitVec("{}_calldatasize".format(self.tx_id), 256)
-            self.concrete = False
-
-        if self.concrete:
-            for calldata_byte in starting_calldata:
-                if type(calldata_byte) == int:
-                    self._calldata.append(BitVecVal(calldata_byte, 8))
-                else:
-                    self._calldata.append(calldata_byte)
-
-    def concretized(self, model):
-        result = []
-        for i in range(
-            get_concrete_int(model.eval(self.calldatasize, model_completion=True))
-        ):
-            result.append(
-                get_concrete_int(model.eval(self._calldata[i], model_completion=True))
-            )
 
+    @property
+    def calldatasize(self) -> ExprRef:
+        """
+        :return: Calldata size for this calldata object
+        """
+        result = self.size
+        if isinstance(result, int):
+            return BitVecVal(result, 256)
         return result
 
-    def get_word_at(self, index: int):
-        return self[index : index + 32]
+    def get_word_at(self, offset: int) -> ExprRef:
+        """ Gets word at offset"""
+        return self[offset : offset + 32]
 
     def __getitem__(self, item: Union[int, slice]) -> Any:
+        if isinstance(item, int) or isinstance(item, ExprRef):
+            return self._load(item)
+
         if isinstance(item, slice):
-            start, step, stop = item.start, item.step, item.stop
+            start = 0 if item.start is None else item.start
+            step = 1 if item.step is None else item.step
+            stop = self.size if item.stop is None else item.stop
+
             try:
-                if start is None:
-                    start = 0
-                if step is None:
-                    step = 1
-                if stop is None:
-                    stop = self.calldatasize
                 current_index = (
                     start if isinstance(start, BitVecRef) else BitVecVal(start, 256)
                 )
-                dataparts = []
+                parts = []
                 while simplify(current_index != stop):
-                    dataparts.append(self[current_index])
+                    parts.append(self._load(current_index))
                     current_index = simplify(current_index + step)
             except Z3Exception:
                 raise IndexError("Invalid Calldata Slice")
 
-            values, constraints = zip(*dataparts)
-            result_constraints = []
-            for c in constraints:
-                result_constraints.extend(c)
-            return simplify(Concat(values)), result_constraints
+            return simplify(Concat(parts))
+
+        raise ValueError
+
+    def _load(self, item: Union[int, ExprRef]) -> Any:
+        raise NotImplementedError()
+
+    @property
+    def size(self) -> Union[ExprRef, int]:
+        """ Returns the exact size of this calldata, this is not normalized"""
+        raise NotImplementedError()
+
+    def concrete(self, model: Model) -> list:
+        """ Returns a concrete version of the calldata using the provided model"""
+        raise NotImplementedError
+
+
+class ConcreteCalldata(BaseCalldata):
+    def __init__(self, tx_id: int, calldata: list):
+        """
+        Initializes the ConcreteCalldata object
+        :param tx_id: Id of the transaction that the calldata is for.
+        :param calldata: The concrete calldata content
+        """
+        self._calldata = calldata
+        super().__init__(tx_id)
 
-        if self.concrete:
+    def _load(self, item: Union[int, ExprRef]) -> Any:
+        if isinstance(item, int):
             try:
-                return self._calldata[get_concrete_int(item)], ()
+                return self._calldata[item]
             except IndexError:
-                return BitVecVal(0, 8), ()
-        else:
-            constraints = [
-                Implies(self._calldata[item] != 0, UGT(self.calldatasize, item))
-            ]
+                return 0
+
+        value = BitVecVal(0x0, 8)
+        for i in range(self.size):
+            value = If(item == i, self._calldata[i], value)
+        return value
+
+    def concrete(self, model: Model) -> list:
+        return self._calldata
+
+    @property
+    def size(self) -> int:
+        return len(self._calldata)
+
+
+class SymbolicCalldata(BaseCalldata):
+    def __init__(self, tx_id: int):
+        """
+        Initializes the SymbolicCalldata object
+        :param tx_id: Id of the transaction that the calldata is for.
+        """
+        self._reads = []
+        self._size = BitVec("calldatasize", 256)
+        super().__init__(tx_id)
+
+    def _load(self, item: Union[int, ExprRef], clean=False) -> Any:
+        x = BitVecVal(item, 256) if isinstance(item, int) else item
+
+        symbolic_base_value = If(
+            x > self._size,
+            BitVecVal(0, 8),
+            BitVec("{}_calldata_{}".format(self.tx_id, str(item)), 8),
+        )
+
+        return_value = symbolic_base_value
+        for r_index, r_value in self._reads:
+            return_value = If(r_index == item, r_value, return_value)
+
+        if not clean:
+            self._reads.append((item, symbolic_base_value))
+        return simplify(return_value)
+
+    def concrete(self, model: Model) -> list:
+        concrete_length = get_concrete_int(model.eval(self.size, model_completion=True))
+        result = []
+        for i in range(concrete_length):
+            value = self._load(i, clean=True)
+            c_value = get_concrete_int(model.eval(value, model_completion=True))
+            result.append(c_value)
+
+        return result
 
-            return self._calldata[item], constraints
+    @property
+    def size(self) -> ExprRef:
+        return self._size
diff --git a/mythril/laser/ethereum/state/environment.py b/mythril/laser/ethereum/state/environment.py
index 91c67d5a..a54e5c42 100644
--- a/mythril/laser/ethereum/state/environment.py
+++ b/mythril/laser/ethereum/state/environment.py
@@ -3,7 +3,7 @@ from typing import Dict
 from z3 import ExprRef, BitVecVal
 
 from mythril.laser.ethereum.state.account import Account
-from mythril.laser.ethereum.state.calldata import Calldata, CalldataType
+from mythril.laser.ethereum.state.calldata import CalldataType, BaseCalldata
 
 
 class Environment:
@@ -15,7 +15,7 @@ class Environment:
         self,
         active_account: Account,
         sender: ExprRef,
-        calldata: Calldata,
+        calldata: BaseCalldata,
         gasprice: ExprRef,
         callvalue: ExprRef,
         origin: ExprRef,
diff --git a/mythril/laser/ethereum/transaction/concolic.py b/mythril/laser/ethereum/transaction/concolic.py
index 0ec88794..6c7a406d 100644
--- a/mythril/laser/ethereum/transaction/concolic.py
+++ b/mythril/laser/ethereum/transaction/concolic.py
@@ -6,7 +6,7 @@ from mythril.laser.ethereum.transaction.transaction_models import (
 )
 from z3 import BitVec
 from mythril.laser.ethereum.state.environment import Environment
-from mythril.laser.ethereum.state.calldata import Calldata, CalldataType
+from mythril.laser.ethereum.state.calldata import CalldataType, ConcreteCalldata
 from mythril.laser.ethereum.state.account import Account
 from mythril.laser.ethereum.state.world_state import WorldState
 from mythril.laser.ethereum.state.global_state import GlobalState
@@ -42,7 +42,7 @@ def execute_message_call(
             code=Disassembly(code),
             caller=caller_address,
             callee_account=open_world_state[callee_address],
-            call_data=Calldata(next_transaction_id, data),
+            call_data=ConcreteCalldata(next_transaction_id, data),
             call_data_type=CalldataType.SYMBOLIC,
             call_value=value,
         )
diff --git a/mythril/laser/ethereum/transaction/symbolic.py b/mythril/laser/ethereum/transaction/symbolic.py
index 88e16780..be1c0ec6 100644
--- a/mythril/laser/ethereum/transaction/symbolic.py
+++ b/mythril/laser/ethereum/transaction/symbolic.py
@@ -3,7 +3,11 @@ from logging import debug
 
 from mythril.disassembler.disassembly import Disassembly
 from mythril.laser.ethereum.cfg import Node, Edge, JumpType
-from mythril.laser.ethereum.state.calldata import CalldataType, Calldata
+from mythril.laser.ethereum.state.calldata import (
+    CalldataType,
+    BaseCalldata,
+    SymbolicCalldata,
+)
 from mythril.laser.ethereum.state.account import Account
 from mythril.laser.ethereum.transaction.transaction_models import (
     MessageCallTransaction,
@@ -32,7 +36,7 @@ def execute_message_call(laser_evm, callee_address: str) -> None:
             origin=BitVec("origin{}".format(next_transaction_id), 256),
             caller=BitVec("caller{}".format(next_transaction_id), 256),
             callee_account=open_world_state[callee_address],
-            call_data=Calldata(next_transaction_id),
+            call_data=SymbolicCalldata(next_transaction_id),
             call_data_type=CalldataType.SYMBOLIC,
             call_value=BitVec("call_value{}".format(next_transaction_id), 256),
         )
diff --git a/mythril/laser/ethereum/transaction/transaction_models.py b/mythril/laser/ethereum/transaction/transaction_models.py
index bef83a2a..7fe73328 100644
--- a/mythril/laser/ethereum/transaction/transaction_models.py
+++ b/mythril/laser/ethereum/transaction/transaction_models.py
@@ -2,7 +2,11 @@ import logging
 from typing import Union
 from mythril.disassembler.disassembly import Disassembly
 from mythril.laser.ethereum.state.environment import Environment
-from mythril.laser.ethereum.state.calldata import Calldata
+from mythril.laser.ethereum.state.calldata import (
+    BaseCalldata,
+    ConcreteCalldata,
+    SymbolicCalldata,
+)
 from mythril.laser.ethereum.state.account import Account
 from mythril.laser.ethereum.state.world_state import WorldState
 from mythril.laser.ethereum.state.global_state import GlobalState
@@ -75,9 +79,9 @@ class BaseTransaction:
         self.caller = caller
         self.callee_account = callee_account
         if call_data is None and init_call_data:
-            self.call_data = Calldata(self.id, call_data)
+            self.call_data = ConcreteCalldata(self.id, call_data)
         else:
-            self.call_data = call_data if isinstance(call_data, Calldata) else None
+            self.call_data = call_data if isinstance(call_data, BaseCalldata) else None
         self.call_data_type = (
             call_data_type
             if call_data_type is not None
diff --git a/tests/laser/state/calldata_test.py b/tests/laser/state/calldata_test.py
index 9bce4a50..3c013f76 100644
--- a/tests/laser/state/calldata_test.py
+++ b/tests/laser/state/calldata_test.py
@@ -1,6 +1,6 @@
 import pytest
-from mythril.laser.ethereum.state.calldata import Calldata
-from z3 import Solver, simplify
+from mythril.laser.ethereum.state.calldata import ConcreteCalldata, SymbolicCalldata
+from z3 import Solver, simplify, BitVec, sat, unsat
 from z3.z3types import Z3Exception
 from mock import MagicMock
 
@@ -13,21 +13,11 @@ uninitialized_test_data = [
 @pytest.mark.parametrize("starting_calldata", uninitialized_test_data)
 def test_concrete_calldata_uninitialized_index(starting_calldata):
     # Arrange
-    calldata = Calldata(0, starting_calldata)
-    solver = Solver()
+    calldata = ConcreteCalldata(0, starting_calldata)
 
     # Act
-    value, constraint1 = calldata[100]
-    value2, constraint2 = calldata.get_word_at(200)
-
-    solver.add(constraint1)
-    solver.add(constraint2)
-
-    solver.check()
-    model = solver.model()
-
-    value = model.eval(value)
-    value2 = model.eval(value2)
+    value = calldata[100]
+    value2 = calldata.get_word_at(200)
 
     # Assert
     assert value == 0
@@ -36,73 +26,65 @@ def test_concrete_calldata_uninitialized_index(starting_calldata):
 
 def test_concrete_calldata_calldatasize():
     # Arrange
-    calldata = Calldata(0, [1, 4, 7, 3, 7, 2, 9])
+    calldata = ConcreteCalldata(0, [1, 4, 7, 3, 7, 2, 9])
     solver = Solver()
 
     # Act
     solver.check()
     model = solver.model()
-
     result = model.eval(calldata.calldatasize)
 
     # Assert
     assert result == 7
 
 
-def test_symbolic_calldata_constrain_index():
+def test_concrete_calldata_constrain_index():
     # Arrange
-    calldata = Calldata(0)
+    calldata = ConcreteCalldata(0, [1, 4, 7, 3, 7, 2, 9])
     solver = Solver()
 
     # Act
-    value, calldata_constraints = calldata[100]
-    constraint = value == 50
-
-    solver.add([constraint] + calldata_constraints)
-
-    solver.check()
-    model = solver.model()
+    value = calldata[2]
+    constraint = value == 3
 
-    value = model.eval(value)
-    calldatasize = model.eval(calldata.calldatasize)
+    solver.add([constraint])
+    result = solver.check()
 
     # Assert
-    assert value == 50
-    assert simplify(calldatasize >= 100)
+    assert str(result) == "unsat"
 
 
-def test_concrete_calldata_constrain_index():
+def test_symbolic_calldata_constrain_index():
     # Arrange
-    calldata = Calldata(0, [1, 4, 7, 3, 7, 2, 9])
+    calldata = SymbolicCalldata(0)
     solver = Solver()
 
     # Act
-    value, calldata_constraints = calldata[2]
-    constraint = value == 3
+    value = calldata[51]
+
+    constraints = [value == 1, calldata.calldatasize == 50]
+
+    solver.add(constraints)
 
-    solver.add([constraint] + calldata_constraints)
     result = solver.check()
 
     # Assert
     assert str(result) == "unsat"
 
 
-def test_concrete_calldata_constrain_index():
-    # Arrange
-    calldata = Calldata(0)
-    mstate = MagicMock()
-    mstate.constraints = []
-    solver = Solver()
+def test_symbolic_calldata_equal_indices():
+    calldata = SymbolicCalldata(0)
 
-    # Act
-    constraints = []
-    value, calldata_constraints = calldata[51]
-    constraints.append(value == 1)
-    constraints.append(calldata.calldatasize == 50)
+    index_a = BitVec("index_a", 256)
+    index_b = BitVec("index_b", 256)
 
-    solver.add(constraints + calldata_constraints)
+    # Act
+    a = calldata[index_a]
+    b = calldata[index_b]
 
-    result = solver.check()
+    s = Solver()
+    s.append(index_a == index_b)
+    s.append(a != b)
 
     # Assert
-    assert str(result) == "unsat"
+    assert unsat == s.check()
diff --git a/tests/testdata/input_contracts/overflow.sol b/tests/testdata/input_contracts/overflow.sol
index d1d3d875..d434b917 100644
--- a/tests/testdata/input_contracts/overflow.sol
+++ b/tests/testdata/input_contracts/overflow.sol
@@ -11,7 +11,7 @@ contract Over {
   }
 
   function sendeth(address _to, uint _value) public returns (bool) {
-    require(balances[msg.sender] - _value >= 0);
+    // require(balances[msg.sender] - _value >= 0);
     balances[msg.sender] -= _value;
     balances[_to] += _value;
     return true;