diff --git a/py_order_utils/builders/base_builder.py b/py_order_utils/builders/base_builder.py
index 16e0577..13853f2 100644
--- a/py_order_utils/builders/base_builder.py
+++ b/py_order_utils/builders/base_builder.py
@@ -1,8 +1,9 @@
 from ..signer import Signer
-from ..utils import normalize_address
+from ..utils import normalize_address, prepend_zx
 from poly_eip712_structs import make_domain, EIP712Struct
 from eth_utils import keccak
 
+
 class BaseBuilder:
     def __init__(
         self, exchange_address: str, chain_id: int, signer: Signer, salt_generator
@@ -29,7 +30,9 @@ def _create_struct_hash(self, order: EIP712Struct):
         """
         Creates an EIP712 compliant struct hash for the Order
         """
-        return "0x" + keccak(order.signable_bytes(domain=self.domain_separator)).hex()
+        return prepend_zx(
+            keccak(order.signable_bytes(domain=self.domain_separator)).hex()
+        )
 
     def sign(self, struct_hash):
         """
diff --git a/py_order_utils/builders/order_builder.py b/py_order_utils/builders/order_builder.py
index 88dec6a..380696a 100644
--- a/py_order_utils/builders/order_builder.py
+++ b/py_order_utils/builders/order_builder.py
@@ -1,7 +1,7 @@
 from ..signer import Signer
 from .base_builder import BaseBuilder
 from .exception import ValidationException
-from ..utils import generate_seed, normalize_address
+from ..utils import generate_seed, normalize_address, prepend_zx
 from ..model.order import Order, SignedOrder, OrderData
 from ..model.sides import BUY, SELL
 from ..model.signatures import EOA, POLY_GNOSIS_SAFE, POLY_PROXY
@@ -59,7 +59,7 @@ def build_order_signature(self, _order: Order) -> str:
         """
         Signs the order
         """
-        return "0x" + self.sign(self._create_struct_hash(_order))
+        return prepend_zx(self.sign(self._create_struct_hash(_order)))
 
     def build_signed_order(self, data: OrderData) -> SignedOrder:
         """
diff --git a/py_order_utils/utils.py b/py_order_utils/utils.py
index 2756d3d..99e1983 100644
--- a/py_order_utils/utils.py
+++ b/py_order_utils/utils.py
@@ -25,3 +25,12 @@ def generate_seed() -> int:
     now = datetime.now().replace(tzinfo=timezone.utc).timestamp()
     return round(now * random())
 
+
+def prepend_zx(in_str: str) -> str:
+    """
+    Prepend 0x to the input string if it is missing
+    """
+    s = in_str
+    if len(s) > 2 and s[:2] != "0x":
+        s = f"0x{s}"
+    return s
diff --git a/setup.py b/setup.py
index 9e014de..6b24d54 100644
--- a/setup.py
+++ b/setup.py
@@ -5,7 +5,7 @@
 
 setuptools.setup(
     name="py_order_utils",
-    version="0.3.1",
+    version="0.3.2",
     author="Polymarket Engineering",
     author_email="engineering@polymarket.com",
     maintainer="Polymarket Engineering",
@@ -18,7 +18,7 @@
         "eth-utils>=4.1.1",
         "eth-account>=0.13.0",
         "poly-eip712-structs",
-        "pytest"
+        "pytest",
     ],
     package_data={
         "py_order_utils": [
diff --git a/tests/test_utils.py b/tests/test_utils.py
index 499297d..57c6254 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -1,5 +1,5 @@
 from unittest import TestCase
-from py_order_utils.utils import generate_seed, normalize_address
+from py_order_utils.utils import generate_seed, normalize_address, prepend_zx
 
 
 class TestUtils(TestCase):
@@ -11,3 +11,10 @@ def test_normalize_address(self):
 
     def test_generate_seed(self):
         self.assertIsNotNone(generate_seed())
+
+    def test_prepend_zx(self):
+        s = "302cd9abd0b5fcaa202a344437ec0b6660da984e24ae9ad915a592a90facf5a51bb8a873cd8d270f070217fea1986531d5eec66f1162a81f66e026db653bf7ce1c"
+        self.assertEqual("0x" + s, prepend_zx(s))
+
+        s = "02ca1d1aa31103804173ad1acd70066cb6c1258a4be6dada055111f9a7ea4e55"
+        self.assertEqual("0x" + s, prepend_zx(s))