diff --git a/packages/api/src/checkTypes.manual.ts b/packages/api/src/checkTypes.manual.ts
index e5dc317cbb..fa8b79b2f0 100644
--- a/packages/api/src/checkTypes.manual.ts
+++ b/packages/api/src/checkTypes.manual.ts
@@ -52,7 +52,7 @@ export default async function test (): Promise<void> {
   // constants has actual value & metadata
   console.log(
     api.consts.balances.creationFee.toHex(),
-    api.consts.balances.creationFee.meta.documentation.map((s) => s.toString()).join('')
+    api.consts.balances.creationFee.meta.documentation.map((s): string => s.toString()).join('')
   );
 
   const transfer = api.tx.balances.transfer(keyring.bob.address, 12345);
diff --git a/packages/api/test/e2e/api/promise-tx.spec.ts b/packages/api/test/e2e/api/promise-tx.spec.ts
index b7a05f420a..2607fe1283 100644
--- a/packages/api/test/e2e/api/promise-tx.spec.ts
+++ b/packages/api/test/e2e/api/promise-tx.spec.ts
@@ -5,6 +5,7 @@
 import Keyring from '@polkadot/keyring';
 import testingPairs from '@polkadot/keyring/testingPairs';
 import WsProvider from '@polkadot/rpc-provider/ws';
+import { u8aToHex } from '@polkadot/util';
 import { randomAsHex } from '@polkadot/util-crypto';
 import { EventRecord, ExtrinsicEra, Hash, Header, Index, SignedBlock } from '@polkadot/types';
 
@@ -55,6 +56,28 @@ describeE2E({
     return api.tx(hex).send(logEvents(done));
   });
 
+  it('invalid hex does throw a catchable exception', async (done): Promise<void> => {
+    const nonce = await api.query.system.accountNonce(keyring.dave.address) as Index;
+    const hex = api.tx.balances
+      .transfer(keyring.eve.address, 12345)
+      .sign(keyring.dave, { nonce })
+      .toHex();
+
+    // change to an invalid signature, 32 * 2 for hex
+    const sigIdx = hex.indexOf(u8aToHex(keyring.dave.publicKey).substr(2)) + 64;
+    const mangled = hex.replace(
+      hex.substr(sigIdx, 32), // first 16 bytes of sig
+      hex.substr(2, 32) // replaced by first 16 bytes of tx
+    );
+
+    try {
+      await api.tx(mangled).send(logEvents(done));
+    } catch (error) {
+      console.error(error);
+      done();
+    }
+  });
+
   it('makes a transfer (sign, then send)', async (done): Promise<() => void> => {
     const nonce = await api.query.system.accountNonce(keyring.dave.address) as Index;
 
@@ -166,6 +189,31 @@ describeE2E({
       });
     });
 
+    it('fails on a transfer with invalid time (via Signer)', async (done): Promise<void> => {
+      const signer: Signer = new SingleAccountSigner(keyring.alice);
+
+      api.setSigner(signer);
+
+      const nonce = await api.query.system.accountNonce(keyring.alice.address) as Index;
+      const signedBlock = await api.rpc.chain.getBlock() as SignedBlock;
+      const currentHeight = signedBlock.block.header.number;
+      const exERA = new ExtrinsicEra({ current: currentHeight, period: 4 });
+      const eraDeath = exERA.asMortalEra.death(currentHeight.toNumber());
+      const blockHash = signedBlock.block.header.hash;
+      const ex = api.tx.balances.transfer(keyring.eve.address, 12345);
+
+      await api.rpc.chain.subscribeNewHead(async (header: Header): Promise<void> => {
+        if (header.blockNumber.toNumber() === eraDeath - 1) {
+          try {
+            await ex.signAndSend(keyring.alice.address, { blockHash, era: exERA, nonce } as any);
+          } catch (error) {
+            expect(error.message).toMatch(/1010: Invalid Transaction \(0\)/);
+            done();
+          }
+        }
+      });
+    });
+
     it('makes a transfer with custom numeric era', async (done): Promise<void> => {
       await api.tx.balances
         .transfer(keyring.eve.address, 12345)
diff --git a/packages/rpc-core/src/index.ts b/packages/rpc-core/src/index.ts
index d4cbf65f4b..4063a0bd70 100644
--- a/packages/rpc-core/src/index.ts
+++ b/packages/rpc-core/src/index.ts
@@ -12,7 +12,7 @@ import { combineLatest, from, Observable, Observer, of, throwError } from 'rxjs'
 import { catchError, map, publishReplay, refCount, switchMap } from 'rxjs/operators';
 import interfaces from '@polkadot/jsonrpc';
 import { Option, StorageChangeSet, StorageData, StorageKey, Vector, createClass, createType } from '@polkadot/types';
-import { ExtError, assert, isFunction, isNull, logger } from '@polkadot/util';
+import { ExtError, assert, isFunction, isNull, isNumber, logger } from '@polkadot/util';
 
 const l = logger('rpc-core');
 
@@ -173,7 +173,15 @@ export default class Rpc implements RpcInterface {
 
     const call = (...values: any[]): Observable<any> => {
       return new Observable((observer: Observer<any>): VoidCallback => {
-        let subscriptionPromise: Promise<number>;
+        let subscriptionPromise: Promise<number | void>;
+
+        const errorHandler = (error: Error): void => {
+          const message = this.createErrorMessage(method, error);
+
+          l.error(message);
+
+          observer.error(new ExtError(message, (error as ExtError).code, undefined));
+        };
 
         try {
           const params = this.formatInputs(method, values);
@@ -187,13 +195,11 @@ export default class Rpc implements RpcInterface {
             observer.next(this.formatOutput(method, params, result));
           };
 
-          subscriptionPromise = this.provider.subscribe(subType, subName, paramsJson, update);
+          subscriptionPromise = this.provider
+            .subscribe(subType, subName, paramsJson, update)
+            .catch(errorHandler);
         } catch (error) {
-          const message = this.createErrorMessage(method, error);
-
-          l.error(message);
-
-          observer.error(new ExtError(message, (error as ExtError).code, undefined));
+          errorHandler(error);
         }
 
         // Teardown logic
@@ -209,10 +215,13 @@ export default class Rpc implements RpcInterface {
           // ```
           // eslint-disable-next-line @typescript-eslint/no-use-before-define
           memoized.delete(...values);
+
           // Unsubscribe from provider
-          subscriptionPromise
+          subscriptionPromise && subscriptionPromise
             .then((subscriptionId): Promise<boolean> =>
-              this.provider.unsubscribe(subType, unsubName, subscriptionId)
+              isNumber(subscriptionId)
+                ? this.provider.unsubscribe(subType, unsubName, subscriptionId)
+                : Promise.resolve(false)
             )
             .catch((error: Error): void => {
               const message = this.createErrorMessage(method, error);