diff --git a/nimbus/core/executor/process_transaction.nim b/nimbus/core/executor/process_transaction.nim
index 65acd71dc..a1537aab6 100644
--- a/nimbus/core/executor/process_transaction.nim
+++ b/nimbus/core/executor/process_transaction.nim
@@ -156,8 +156,9 @@ proc processBeaconBlockRoot*(vmState: BaseVMState, beaconRoot: Hash256):
     )
 
   # runComputation a.k.a syscall/evm.call
-  if call.runComputation().isError:
-    return err("processBeaconBlockRoot: syscall error")
+  let res = call.runComputation()
+  if res.isError:
+    return err("processBeaconBlockRoot: " & res.error)
 
   statedb.persist(clearEmptyAccount = true, clearCache = false)
   ok()
diff --git a/nimbus/transaction/call_common.nim b/nimbus/transaction/call_common.nim
index 8c680109e..2cda33525 100644
--- a/nimbus/transaction/call_common.nim
+++ b/nimbus/transaction/call_common.nim
@@ -47,7 +47,7 @@ type
   # Standard call result.  (Some fields are beyond what EVMC can return,
   # and must only be used from tests because they will not always be set).
   CallResult* = object
-    isError*:         bool              # True if the call failed.
+    error*:           string            # Something if the call failed.
     gasUsed*:         GasInt            # Gas used by the call.
     contractAddress*: EthAddress        # Created account (when `isCreate`).
     output*:          seq[byte]         # Output data.
@@ -55,6 +55,9 @@ type
     stack*:           Stack             # EVM stack on return (for test only).
     memory*:          Memory            # EVM memory on return (for test only).
 
+func isError*(cr: CallResult): bool =
+  cr.error.len > 0
+
 proc hostToComputationMessage*(msg: EvmcMessage): Message =
   Message(
     kind:            CallKind(msg.kind.ord),
@@ -182,7 +185,7 @@ proc setupHost(call: CallParams): TransactionHost =
     let cMsg = hostToComputationMessage(host.msg)
     host.computation = newComputation(vmState, call.sysCall, cMsg, code)
 
-    shallowCopy(host.code, code)
+    host.code = system.move(code)
 
   else:
     if call.input.len > 0:
@@ -284,9 +287,10 @@ proc finishRunningComputation(host: TransactionHost, call: CallParams): CallResu
   let gasUsed = host.msg.gas - gasRemaining
   host.vmState.captureEnd(c, c.output, gasUsed, c.errorOpt)
 
-  result.isError = c.isError
+  if c.isError:
+    result.error = c.error.info
   result.gasUsed = call.gasLimit - gasRemaining
-  shallowCopy(result.output, c.output)
+  result.output = system.move(c.output)
   result.contractAddress = if call.isCreate: c.msg.contractAddress
                            else: default(HostAddress)
   result.logEntries = host.vmState.stateDB.logEntries()
diff --git a/nimbus/transaction/call_evm.nim b/nimbus/transaction/call_evm.nim
index 60efa60bf..6e86669af 100644
--- a/nimbus/transaction/call_evm.nim
+++ b/nimbus/transaction/call_evm.nim
@@ -18,6 +18,9 @@ import
   ../common/common,
   ./call_common
 
+export
+  call_common
+
 type
   RpcCallData* = object
     source*        : Option[EthAddress]