diff --git a/tests/test_quantity.nim b/tests/test_quantity.nim
index beb2481..e29fcdb 100644
--- a/tests/test_quantity.nim
+++ b/tests/test_quantity.nim
@@ -23,8 +23,10 @@ suite "JSON-RPC Quantity":
         resUInt256Ref[] == validQuantity.u256
 
   test "Invalid Quantity/UInt256/ref UInt256":
+    # TODO once https://github.com/status-im/nimbus-eth2/pull/3850 addressed,
+    # re-add "0x0400" test case as invalid.
     for invalidStr in [
-        "", "1234", "01234", "x1234", "0x", "0x0400", "ff"]:
+        "", "1234", "01234", "x1234", "0x", "ff"]:
       template checkInvalids(typeName: untyped) =
         var resQuantity: `typeName`
         try:
diff --git a/web3/conversions.nim b/web3/conversions.nim
index f4f4a44..fa59846 100644
--- a/web3/conversions.nim
+++ b/web3/conversions.nim
@@ -21,7 +21,13 @@ template invalidQuantityPrefix(s: string): bool =
   #
   # strutils.parseHexStr treats 0x as optional otherwise. UInt256.parse treats
   # standalone "0x" as valid input.
-  (not s.startsWith "0x") or s == "0x" or (s != "0x0" and s.startsWith "0x0")
+
+  # TODO https://github.com/status-im/nimbus-eth2/pull/3850
+  # requiring 0x prefis is okay, but can't yet enforce no-leading-zeros
+  when false:
+    (not s.startsWith "0x") or s == "0x" or (s != "0x0" and s.startsWith "0x0")
+  else:
+    (not s.startsWith "0x") or s == "0x"
 
 func `%`*(n: Int256|UInt256): JsonNode = %("0x" & n.toHex)