diff --git a/packages/account-sdk/src/sign/base-account/Signer.test.ts b/packages/account-sdk/src/sign/base-account/Signer.test.ts
index 78570225..a73b4474 100644
--- a/packages/account-sdk/src/sign/base-account/Signer.test.ts
+++ b/packages/account-sdk/src/sign/base-account/Signer.test.ts
@@ -431,9 +431,14 @@ describe('Signer', () => {
         params: [],
       };
 
+      // eth_sendTransaction requires a valid 32-byte tx hash response
+      const mockValue = method === 'eth_sendTransaction'
+        ? '0x' + 'a'.repeat(64)  // valid 32-byte tx hash
+        : '0xSignature';
+
       (decryptContent as Mock).mockResolvedValueOnce({
         result: {
-          value: '0xSignature',
+          value: mockValue,
         },
       });
 
diff --git a/packages/account-sdk/src/sign/base-account/Signer.ts b/packages/account-sdk/src/sign/base-account/Signer.ts
index 6ccbb8f2..2cc569b1 100644
--- a/packages/account-sdk/src/sign/base-account/Signer.ts
+++ b/packages/account-sdk/src/sign/base-account/Signer.ts
@@ -428,6 +428,17 @@ export class Signer {
         this.callback?.('accountsChanged', this.accounts);
         break;
       }
+      case 'eth_sendTransaction': {
+        const txHash = result.value as string;
+        // Validate that the response is a 32-byte tx hash (64 hex chars + 0x prefix = 66 chars)
+        // If the popup returns a 65-byte ECDSA signature instead of a tx hash, throw an error
+        if (typeof txHash === 'string' && txHash.startsWith('0x') && txHash.length !== 66) {
+          throw standardErrors.rpc.internal(
+            `eth_sendTransaction returned invalid response: expected 32-byte tx hash (66 chars) but got ${txHash.length} chars. The popup may have returned a signature instead of a transaction hash.`
+          );
+        }
+        break;
+      }
       default:
         break;
     }