diff --git a/processor/ethereum/router/contracts/IRouter.sol b/processor/ethereum/router/contracts/IRouter.sol
index 57994f8d..c22bef3c 100644
--- a/processor/ethereum/router/contracts/IRouter.sol
+++ b/processor/ethereum/router/contracts/IRouter.sol
@@ -45,6 +45,8 @@ interface IRouterWithoutCollisions {
   /// @param amount The amount which escaped
   event Escaped(address indexed coin, uint256 amount);
 
+  /// @notice The Serai key verifying the signature wasn't set
+  error SeraiKeyWasNone();
   /// @notice The key for Serai was invalid
   /// @dev This is incomplete and not always guaranteed to be thrown upon an invalid key
   error InvalidSeraiKey();
diff --git a/processor/ethereum/router/contracts/Router.sol b/processor/ethereum/router/contracts/Router.sol
index e0bc77bb..c3f6befa 100644
--- a/processor/ethereum/router/contracts/Router.sol
+++ b/processor/ethereum/router/contracts/Router.sol
@@ -137,7 +137,7 @@ contract Router is IRouterWithoutCollisions {
       The Schnorr contract should already reject this public key yet it's best to be explicit.
     */
     if (key == bytes32(0)) {
-      revert InvalidSignature();
+      revert SeraiKeyWasNone();
     }
 
     message = msg.data;
@@ -266,7 +266,7 @@ contract Router is IRouterWithoutCollisions {
   function inInstruction(address coin, uint256 amount, bytes memory instruction) external payable {
     // Check there is an active key
     if (_seraiKey == bytes32(0)) {
-      revert InvalidSeraiKey();
+      revert SeraiKeyWasNone();
     }
 
     // Don't allow further InInstructions once the escape hatch has been invoked
diff --git a/processor/ethereum/router/src/tests/mod.rs b/processor/ethereum/router/src/tests/mod.rs
index f66a70f8..da79e956 100644
--- a/processor/ethereum/router/src/tests/mod.rs
+++ b/processor/ethereum/router/src/tests/mod.rs
@@ -367,10 +367,46 @@ async fn test_constructor() {
 #[tokio::test]
 async fn test_confirm_next_serai_key() {
   let mut test = Test::new().await;
-  // TODO: Check all calls fail at this time, including inInstruction
   test.confirm_next_serai_key().await;
 }
 
+#[tokio::test]
+async fn test_no_serai_key() {
+  // Before we confirm a key, any operations requiring a signature shouldn't work
+  {
+    let mut test = Test::new().await;
+
+    // Corrupt the test's state so we can obtain signed TXs
+    test.state.key = Some(test_key());
+
+    assert!(matches!(
+      test.call_and_decode_err(test.update_serai_key_tx().1).await,
+      IRouterErrors::SeraiKeyWasNone(IRouter::SeraiKeyWasNone {})
+    ));
+    /* TODO
+    assert!(matches!(
+      test.call_and_decode_err(test.execute_tx()).await,
+      IRouterErrors::SeraiKeyWasNone(IRouter::SeraiKeyWasNone {})
+    ));
+    */
+    assert!(matches!(
+      test.call_and_decode_err(test.escape_hatch_tx(Address::ZERO)).await,
+      IRouterErrors::SeraiKeyWasNone(IRouter::SeraiKeyWasNone {})
+    ));
+  }
+
+  // And if there's no key to confirm, any operations requiring a signature shouldn't work
+  {
+    let mut test = Test::new().await;
+    test.confirm_next_serai_key().await;
+    test.state.next_key = Some(test_key());
+    assert!(matches!(
+      test.call_and_decode_err(test.confirm_next_serai_key_tx()).await,
+      IRouterErrors::SeraiKeyWasNone(IRouter::SeraiKeyWasNone {})
+    ));
+  }
+}
+
 #[tokio::test]
 async fn test_update_serai_key() {
   let mut test = Test::new().await;
@@ -421,7 +457,7 @@ async fn test_no_in_instruction_before_key() {
   let (_coin, _amount, _shorthand, tx) = test.eth_in_instruction_tx();
   assert!(matches!(
     test.call_and_decode_err(tx).await,
-    IRouterErrors::InvalidSeraiKey(IRouter::InvalidSeraiKey {})
+    IRouterErrors::SeraiKeyWasNone(IRouter::SeraiKeyWasNone {})
   ));
 }