diff --git a/src/dapp-tests/integration/tests.sh b/src/dapp-tests/integration/tests.sh
index 8ebe92349..84b026bf2 100755
--- a/src/dapp-tests/integration/tests.sh
+++ b/src/dapp-tests/integration/tests.sh
@@ -1,5 +1,7 @@
 #! /usr/bin/env bash
 
+set -eo pipefail
+
 # ------------------------------------------------
 #                CONFIGURATION
 # ------------------------------------------------
@@ -460,6 +462,55 @@ test_calldata_19() {
     assert_equals "0xc2985578" "$output"
 }
 
+test_calldata_20() {
+    local output
+    output=$(seth calldata 'foo(bytes32, bytes4, bytes16)' '0x' '0x' '0x')
+
+    assert_equals "0x1765a16e000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000" "$output"
+}
+
+test_sig_1() {
+    assert_equals "0xd2ce7d65" "$(seth sig 'outboundTransfer(address,address,uint256,uint256,uint256,bytes)')"
+}
+
+test_sig_2() {
+    assert_equals "0x6a4f4b05" "$(seth sig 'setKeepers(address[],bool[])')"
+}
+
+test_sig_3() {
+    assert_equals "0xf837dc72" "$(seth sig 'payAll(bytes12,uint128)')"
+}
+
+test_sig_4() {
+    assert_equals "0xd2ce7d65" "$(seth sig 'outboundTransfer(address,address,uint,uint,uint,bytes memory)')"
+}
+
+test_sig_5() {
+    assert_equals "0xe548799c" "$(seth sig 'registerCrowdsale(address,address,uint256[8])')"
+}
+
+# tuples currently broken: https://github.com/dapphub/dapptools/issues/861
+todo_sig_6() {
+    assert_equals "0x5cc5e3d9" "$(seth sig 'createIncentive((address,address,uint256,uint256,address),uint256)')"
+}
+
+# ignored for now due to https://github.com/dapphub/dapptools/issues/861
+todo_sig_fuzz() {
+    echo
+    for _ in $(seq "$FUZZ_RUNS"); do
+      id=$(mod "$(uint256)" 236272)
+      sig=$(curl -s "https://www.4byte.directory/api/v1/signatures/$id/")
+      [[ "$sig" == '{"detail":"Not found."}' ]] && continue
+      text=$(echo "$sig" | jq -r .text_signature)
+      hex=$(echo "$sig" | jq -r .hex_signature)
+      echo "checking ($id): $text"
+
+      local actual
+      actual=$(seth sig "$text")
+      assert_equals "$hex" "$actual"
+    done
+}
+
 test_keccak_1() {
   local output
   output=$(seth keccak 0xcafe)
diff --git a/src/hevm/CHANGELOG.md b/src/hevm/CHANGELOG.md
index 56d41738a..0a7ef1df9 100644
--- a/src/hevm/CHANGELOG.md
+++ b/src/hevm/CHANGELOG.md
@@ -15,6 +15,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Clearer display for the invalid opcode (`0xfe`) in debug view
 - Better error messages when trying to deploy unlinked bytecode
+- `bytesX` arguments to `hevm abiencode` are automatically padded
 
 ### Fixed
 
diff --git a/src/hevm/src/EVM/ABI.hs b/src/hevm/src/EVM/ABI.hs
index b7809ac21..b459b2073 100644
--- a/src/hevm/src/EVM/ABI.hs
+++ b/src/hevm/src/EVM/ABI.hs
@@ -483,9 +483,13 @@ instance Read Boolz where
   readsPrec n (_:t) = readsPrec n t
 
 makeAbiValue :: AbiType -> String -> AbiValue
-makeAbiValue typ str = case readP_to_S (parseAbiValue typ) str of
+makeAbiValue typ str = case readP_to_S (parseAbiValue typ) (padStr str) of
   [(val,"")] -> val
   _ -> error $  "could not parse abi argument: " ++ str ++ " : " ++ show typ
+  where
+    padStr = case typ of
+      (AbiBytesType n) -> padRight' (2 * n + 2) -- +2 is for the 0x prefix
+      _ -> id
 
 parseAbiValue :: AbiType -> ReadP AbiValue
 parseAbiValue (AbiUIntType n) = do W256 w <- readS_to_P reads
diff --git a/src/hevm/src/EVM/Types.hs b/src/hevm/src/EVM/Types.hs
index dfb2be0a0..fdd2368de 100644
--- a/src/hevm/src/EVM/Types.hs
+++ b/src/hevm/src/EVM/Types.hs
@@ -463,6 +463,9 @@ padLeft n xs = BS.replicate (n - BS.length xs) 0 <> xs
 padRight :: Int -> ByteString -> ByteString
 padRight n xs = xs <> BS.replicate (n - BS.length xs) 0
 
+padRight' :: Int -> String -> String
+padRight' n xs = xs <> replicate (n - length xs) '0'
+
 -- | Right padding  / truncating
 truncpad :: Int -> [SWord 8] -> [SWord 8]
 truncpad n xs = if m > n then take n xs
diff --git a/src/seth/CHANGELOG.md b/src/seth/CHANGELOG.md
index 4b2ea6403..7998007e0 100644
--- a/src/seth/CHANGELOG.md
+++ b/src/seth/CHANGELOG.md
@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
+- `bytesX` arguments to `seth calldata` are automatically padded
 - `seth 4byte` command returns the response from querying [4byte.directory](https://www.4byte.directory/) for a given function signature
 - `seth 4byte-decode` command queries 4byte.directory for matching function signatures, uses one to decode the calldata, and prints the decoded calldata
 - `seth 4byte-event` command returns the response from querying 4byte.directory for a given event topic
diff --git a/src/seth/libexec/seth/seth-sig b/src/seth/libexec/seth/seth-sig
index 13b535b1d..8d4ab663d 100755
--- a/src/seth/libexec/seth/seth-sig
+++ b/src/seth/libexec/seth/seth-sig
@@ -8,14 +8,22 @@ set -e
 
 # Get ABI from input
 abi=$(seth --abi-function-json "$1")
-inputs=$(echo $abi | jq '.inputs[] | .type')
+inputs=$(echo "$abi" | jq '.inputs[] | .type')
 
 # Generate dummy args
 args=()
 for input in $inputs; do
   type="${input//\"}" # remove leading and trailing quotes from the JSON
-  end=${type: -2} # get the last two characters to check for array types
-  [ $end = "[]"  ] && arg="[]" || arg=0 # use [] for array types and 0 otherwise
+  end=${type: -1} # get the last character to check for array types
+  if [[ "$end" = "]" ]]; then
+    arg="[]"
+  elif [[ "$type" =~ ^byte.*$ ]]; then
+    arg="0x"
+  elif [[ "$type" =~ ^string$ ]]; then
+    arg='""'
+  else
+    arg=0
+  fi
   args+=(--arg "$arg")
 done