diff --git a/packages/bcp/src/cosmwasmconnection.spec.ts b/packages/bcp/src/cosmwasmconnection.spec.ts
index 6272c09a..2b867e6d 100644
--- a/packages/bcp/src/cosmwasmconnection.spec.ts
+++ b/packages/bcp/src/cosmwasmconnection.spec.ts
@@ -1,4 +1,8 @@
-import { CosmosAddressBech32Prefix, decodeSignature } from "@cosmwasm/sdk";
+import {
+  CosmosAddressBech32Prefix,
+  decodeSignature,
+  makeSecp256k1SignatureFromFixedLength,
+} from "@cosmwasm/sdk";
 import {
   Account,
   Address,
@@ -15,7 +19,7 @@ import {
   TransactionId,
   TransactionState,
 } from "@iov/bcp";
-import { Random, Secp256k1, Secp256k1Signature, Sha256 } from "@iov/crypto";
+import { Random, Secp256k1, Sha256 } from "@iov/crypto";
 import { Bech32, Encoding } from "@iov/encoding";
 import { HdPaths, Secp256k1HdWallet, UserProfile } from "@iov/keycontrol";
 import { assert } from "@iov/utils";
@@ -473,7 +477,7 @@ describe("CosmWasmConnection", () => {
       const { pubkey, signature } = decodeSignature(encodeFullSignature(signatures[0]));
       const prehashed = new Sha256(signBytes).digest();
       const valid = await Secp256k1.verifySignature(
-        new Secp256k1Signature(signature.slice(0, 32), signature.slice(32, 64)),
+        makeSecp256k1SignatureFromFixedLength(signature),
         prehashed,
         pubkey,
       );
diff --git a/packages/sdk/package.json b/packages/sdk/package.json
index a45a3bee..516a50f8 100644
--- a/packages/sdk/package.json
+++ b/packages/sdk/package.json
@@ -41,9 +41,11 @@
     "@iov/crypto": "^2.0.2",
     "@iov/encoding": "^2.0.2",
     "@iov/utils": "^2.0.2",
-    "axios": "^0.19.0"
+    "axios": "^0.19.0",
+    "bn.js": "^5.1.1"
   },
   "devDependencies": {
+    "@types/bn.js": "^4.11.6",
     "readonly-date": "^1.0.0"
   }
 }
diff --git a/packages/sdk/src/index.ts b/packages/sdk/src/index.ts
index 371c4cbe..bd5a46fd 100644
--- a/packages/sdk/src/index.ts
+++ b/packages/sdk/src/index.ts
@@ -23,5 +23,9 @@ export {
   encodeSecp256k1Pubkey,
 } from "./pubkey";
 export { findSequenceForSignedTx } from "./sequence";
-export { encodeSecp256k1Signature, decodeSignature } from "./signature";
+export {
+  encodeSecp256k1Signature,
+  decodeSignature,
+  makeSecp256k1SignatureFromFixedLength,
+} from "./signature";
 export { SigningCallback, SigningCosmWasmClient, ExecuteResult } from "./signingcosmwasmclient";
diff --git a/packages/sdk/src/pen.spec.ts b/packages/sdk/src/pen.spec.ts
index 57c71c78..68a514c2 100644
--- a/packages/sdk/src/pen.spec.ts
+++ b/packages/sdk/src/pen.spec.ts
@@ -1,8 +1,8 @@
-import { Secp256k1, Secp256k1Signature, Sha256 } from "@iov/crypto";
+import { Secp256k1, Sha256 } from "@iov/crypto";
 import { Encoding } from "@iov/encoding";
 
 import { Secp256k1Pen } from "./pen";
-import { decodeSignature } from "./signature";
+import { decodeSignature, makeSecp256k1SignatureFromFixedLength } from "./signature";
 
 const { fromHex } = Encoding;
 
@@ -37,7 +37,7 @@ describe("Sec256k1Pen", () => {
       const { pubkey, signature } = decodeSignature(await pen.sign(data));
 
       const valid = await Secp256k1.verifySignature(
-        new Secp256k1Signature(signature.slice(0, 32), signature.slice(32, 64)),
+        makeSecp256k1SignatureFromFixedLength(signature),
         new Sha256(data).digest(),
         pubkey,
       );
diff --git a/packages/sdk/src/sequence.ts b/packages/sdk/src/sequence.ts
index 8a53e897..9c2ef647 100644
--- a/packages/sdk/src/sequence.ts
+++ b/packages/sdk/src/sequence.ts
@@ -1,7 +1,7 @@
-import { Secp256k1, Secp256k1Signature, Sha256 } from "@iov/crypto";
+import { Secp256k1, Sha256 } from "@iov/crypto";
 
 import { makeSignBytes } from "./encoding";
-import { decodeSignature } from "./signature";
+import { decodeSignature, makeSecp256k1SignatureFromFixedLength } from "./signature";
 import { CosmosSdkTx } from "./types";
 
 /**
@@ -26,7 +26,7 @@ export async function findSequenceForSignedTx(
   if (!firstSignature) throw new Error("Signature missing in tx");
 
   const { pubkey, signature } = decodeSignature(firstSignature);
-  const secp256keSignature = new Secp256k1Signature(signature.slice(0, 32), signature.slice(32, 64));
+  const secp256keSignature = makeSecp256k1SignatureFromFixedLength(signature);
 
   for (let s = min; s < upperBound; s++) {
     // console.log(`Trying sequence ${s}`);
diff --git a/packages/sdk/src/signature.ts b/packages/sdk/src/signature.ts
index d31eb119..daa2750c 100644
--- a/packages/sdk/src/signature.ts
+++ b/packages/sdk/src/signature.ts
@@ -1,4 +1,6 @@
+import { Secp256k1Signature } from "@iov/crypto";
 import { Encoding } from "@iov/encoding";
+import BN from "bn.js";
 
 import { encodeSecp256k1Pubkey } from "./pubkey";
 import { pubkeyType, StdSignature } from "./types";
@@ -37,3 +39,10 @@ export function decodeSignature(
       throw new Error("Unsupported pubkey type");
   }
 }
+
+// TODO: use Secp256k1Signature.fromFixedLength once this is published https://github.com/iov-one/iov-core/pull/1401
+export function makeSecp256k1SignatureFromFixedLength(signature: Uint8Array): Secp256k1Signature {
+  const unpaddedR = Uint8Array.from(new BN(signature.slice(0, 32)).toArray());
+  const unpaddedS = Uint8Array.from(new BN(signature.slice(32, 64)).toArray());
+  return new Secp256k1Signature(unpaddedR, unpaddedS);
+}
diff --git a/packages/sdk/types/index.d.ts b/packages/sdk/types/index.d.ts
index 4b2c4d8d..01ee1519 100644
--- a/packages/sdk/types/index.d.ts
+++ b/packages/sdk/types/index.d.ts
@@ -22,5 +22,9 @@ export {
   encodeSecp256k1Pubkey,
 } from "./pubkey";
 export { findSequenceForSignedTx } from "./sequence";
-export { encodeSecp256k1Signature, decodeSignature } from "./signature";
+export {
+  encodeSecp256k1Signature,
+  decodeSignature,
+  makeSecp256k1SignatureFromFixedLength,
+} from "./signature";
 export { SigningCallback, SigningCosmWasmClient, ExecuteResult } from "./signingcosmwasmclient";
diff --git a/packages/sdk/types/signature.d.ts b/packages/sdk/types/signature.d.ts
index c23e7167..16c7e432 100644
--- a/packages/sdk/types/signature.d.ts
+++ b/packages/sdk/types/signature.d.ts
@@ -1,3 +1,4 @@
+import { Secp256k1Signature } from "@iov/crypto";
 import { StdSignature } from "./types";
 /**
  * Takes a binary pubkey and signature to create a signature object
@@ -12,3 +13,4 @@ export declare function decodeSignature(
   readonly pubkey: Uint8Array;
   readonly signature: Uint8Array;
 };
+export declare function makeSecp256k1SignatureFromFixedLength(signature: Uint8Array): Secp256k1Signature;