diff --git a/tests/byzantium/eip198_modexp_precompile/test_modexp.py b/tests/byzantium/eip198_modexp_precompile/test_modexp.py
index 5d103fbf59..55229877a7 100644
--- a/tests/byzantium/eip198_modexp_precompile/test_modexp.py
+++ b/tests/byzantium/eip198_modexp_precompile/test_modexp.py
@@ -16,6 +16,9 @@
     Transaction,
     compute_create_address,
 )
+from execution_testing.base_types.base_types import (
+    FixedSizeBytes,
+)
 
 from .helpers import ModExpInput, ModExpOutput
 
@@ -146,35 +149,32 @@
             id="EIP-198-case5-raw-input",
         ),
         # different declared moduli lengths and parities
-        pytest.param(
-            ModExpInput(
-                base="1234",
-                exponent="234",
-                modulus="1000",
-                declared_modulus_length=256,
-            ),
-            ModExpOutput(
-                returned_data=Bytes(
-                    "07be9ec040921bf6ffa9faad54b5e88c503ea4511cc15505e36fc9569cf20698"
-                    "933819b8c4b15e52a51f64261954708f55432c5a7011dc7d1787c64a8ece6f20"
-                    "65772d1dbc3ea9e96e3f55eeec7477bc92cb587ae416c8316fb3fa825ee25410"
-                    "811fad4f98ade2eaa665b48e930247bb30b25100000000000000000000000000"
-                    + (256 - 4 * 32)
-                    * "00"
-                )
-            ),
-            id="EIP-198-case1-mod-power2-declared-length-256-bytes",
-        ),
-        pytest.param(
-            ModExpInput(
-                base="1234",
-                exponent="234",
-                modulus="1010",
-                declared_modulus_length=128,
-            ),
-            ModExpOutput(returned_data=Bytes("00") + Bytes(hex(2**1014))),
-            id="EIP-198-case1-mod-even-declared-length-128-bytes",
-        ),
+        *[
+            pytest.param(
+                ModExpInput(
+                    base="1234",
+                    exponent="234",
+                    modulus="1000" if parity == "power2" else "1010",
+                    declared_modulus_length=width,
+                ),
+                ModExpOutput(
+                    returned_data=FixedSizeBytes[width](  # type: ignore
+                        (
+                            (0x1234**0x234)
+                            % (
+                                (0x1000 if parity == "power2" else 0x1010)
+                                # declared `width` bitshifts modulus left.
+                                << ((width - 2) * 8)
+                            )
+                        ),
+                        left_padding=True,
+                    )
+                ),
+                id=f"EIP-198-case1-mod-{parity}-declared-length-{width}-bytes",
+            )
+            for width in [64, 128, 256, 512]
+            for parity in ["power2", "even"]
+        ],
         # out of gas cases
         pytest.param(
             Bytes(