diff --git a/eth/common/eth_types_rlp.nim b/eth/common/eth_types_rlp.nim
index 1a12cd9..9110ee2 100644
--- a/eth/common/eth_types_rlp.nim
+++ b/eth/common/eth_types_rlp.nim
@@ -318,14 +318,11 @@ proc append*(w: var RlpWriter, h: BlockHeader) =
   var len = 15
   if h.fee.isSome: inc len
   if h.withdrawalsRoot.isSome:
-    if h.fee.isNone:
-      raise newException(RlpError, "baseFee expected")
+    doAssert(h.fee.isSome, "baseFee expected")
     inc len
   if h.excessDataGas.isSome:
-    if h.fee.isNone:
-      raise newException(RlpError, "baseFee expected")
-    if h.withdrawalsRoot.isNone:
-      raise newException(RlpError, "withdrawalsRoot expected")
+    doAssert(h.fee.isSome, "baseFee expected")
+    doAssert(h.withdrawalsRoot.isSome, "withdrawalsRoot expected")
     inc len
   w.startList(len)
   for k, v in fieldPairs(h):
diff --git a/tests/rlp/test_rlp_codec.nim b/tests/rlp/test_rlp_codec.nim
index 6edffff..51f1397 100644
--- a/tests/rlp/test_rlp_codec.nim
+++ b/tests/rlp/test_rlp_codec.nim
@@ -2,7 +2,7 @@
 
 import
   std/[os, strutils],
-  stew/[io2, results],
+  stew/[io2, results, shims/stddefects],
   unittest2,
   ../../eth/[rlp, common]
 
@@ -67,7 +67,7 @@ suite "BlockHeader roundtrip test":
   
   test "Header + none(baseFee) + some(withdrawalsRoot)":
     let h = BlockHeader(withdrawalsRoot: some(Hash256()))
-    expect RlpError:
+    expect AssertionDefect:
       roundTrip(h)
   
   test "Header + none(baseFee) + some(withdrawalsRoot) + some(excessDataGas)":
@@ -75,14 +75,14 @@ suite "BlockHeader roundtrip test":
       withdrawalsRoot: some(Hash256()), 
       excessDataGas: some(1.u256)
     )
-    expect RlpError:
+    expect AssertionDefect:
       roundTrip(h)
   
   test "Header + none(baseFee) + none(withdrawalsRoot) + some(excessDataGas)":
     let h = BlockHeader(      
       excessDataGas: some(1.u256)
     )
-    expect RlpError:
+    expect AssertionDefect:
       roundTrip(h)
   
   test "Header + some(baseFee) + none(withdrawalsRoot) + some(excessDataGas)":
@@ -90,7 +90,7 @@ suite "BlockHeader roundtrip test":
       fee: some(2.u256),
       excessDataGas: some(1.u256)
     )
-    expect RlpError:
+    expect AssertionDefect:
       roundTrip(h)
       
   test "Header + some(baseFee) + some(withdrawalsRoot)":