diff --git a/CHANGELOG.md b/CHANGELOG.md
index 30195d5364..7c16c3e5ce 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,19 +2,20 @@
 
 - Add support for `api.rpc.chain.subscribeAllHeads` (not just best) (Thanks to https://github.com/jak-pan)
 - Add support for `api.rpc.engine.*` for manual seal support
-- Expand `.toHuman` on ExtrinsicEra, SubmittableResult & Vote
+- Expand `.toHuman` on `ExtrinsicEra`, `SubmittableResult` & `Vote`
 - Remove `GenericDigestItem`, the `DigestItem` is now a type interface via `@polkadot/types/interfaces`
 - Move `H160`, `H256` & `H512` to interfaces in `@polkadot/types/interfaces`
 - Align construction of unknown types via `registry.get` e.g. in Events, warn on detection, throw on use
-- Expose static with on `UInt`, `Int` & `U8aFixed` classes with optional type name override
+- Expose static `.with` on `UInt`, `Int` & `U8aFixed` classes with optional type name override
+- `UInt` & `Int` now does source bitLength checks upon construction
 - Support for arbitrary UInt types via `UInt<bitLength>` definitions
 - Add `api.injectMetadata(metadata)` to initialize with a specific version
 - The api now checks for runtime upgrades, decorating with new metadata
-- One-lners are normally not mentioned, however the [11 Jan 2019](https://github.com/polkadot-js/api/issues/574) is fixed
+- Remove old [11 Jan 2019](https://github.com/polkadot-js/api/issues/574) extrinsic length hack
 
 # 1.3.1 Feb 18, 2020
 
-- Add `@types/bn.js` as a normal dependency, exposed in `*.d.ts` ((Thanks to https://github.com/monitz87)
+- Add `@types/bn.js` as a normal dependency, exposed in `*.d.ts` (Thanks to https://github.com/monitz87)
 - Type generation scripts (including `polkadot-types-from-{chain,defs}`) has been moved to the `@polkadot/typegen` package
 - The `@polkadot/types/codec/create` has been moved to `@polkadot/types/create`, imports from `@polkadot/types` are unaffected
 - Expose chain properties on registry (and use for API type formatting)
diff --git a/packages/types/src/codec/AbstractInt.ts b/packages/types/src/codec/AbstractInt.ts
index 6d0326fe49..ee1e097df1 100644
--- a/packages/types/src/codec/AbstractInt.ts
+++ b/packages/types/src/codec/AbstractInt.ts
@@ -6,7 +6,7 @@ import { H256 } from '../interfaces/runtime';
 import { AnyNumber, Codec, Registry } from '../types';
 
 import BN from 'bn.js';
-import { bnToBn, formatNumber, hexToBn, isHex, isString, isU8a, u8aToBn } from '@polkadot/util';
+import { assert, bnToBn, formatNumber, hexToBn, isHex, isString, isU8a, u8aToBn } from '@polkadot/util';
 import { blake2AsU8a } from '@polkadot/util-crypto';
 
 import Raw from './Raw';
@@ -38,6 +38,8 @@ export default abstract class AbstractInt extends BN implements Codec {
     this._bitLength = bitLength;
     this._isHexJson = isHexJson;
     this._isNegative = isNegative;
+
+    assert(super.bitLength() <= bitLength, `${this.toRawType()}: Input too large. Found input with ${super.bitLength()} bits, expected ${bitLength}`);
   }
 
   /** @internal */
diff --git a/packages/types/src/codec/UInt.spec.ts b/packages/types/src/codec/UInt.spec.ts
index 5310c621e1..fe45b8c13a 100644
--- a/packages/types/src/codec/UInt.spec.ts
+++ b/packages/types/src/codec/UInt.spec.ts
@@ -10,6 +10,12 @@ import UInt from './UInt';
 describe('UInt', (): void => {
   const registry = new TypeRegistry();
 
+  it('fails on a number that is too large for the bits specified', (): void => {
+    expect(
+      (): UInt => new UInt(registry, '12345678901234567890123456789012345678901234567890', 32)
+    ).toThrow('u32: Input too large. Found input with 164 bits, expected 32');
+  });
+
   it('provides a toBn interface', (): void => {
     expect(
       new UInt(registry, 987).toBn().toNumber()