diff --git a/extension/js/common/core/msg-block-parser.ts b/extension/js/common/core/msg-block-parser.ts
index 5a75a278885..b9cbe901feb 100644
--- a/extension/js/common/core/msg-block-parser.ts
+++ b/extension/js/common/core/msg-block-parser.ts
@@ -162,6 +162,34 @@ export class MsgBlockParser {
     );
   }
 
+  /**
+   * Find an end marker that is NOT on a quoted line (lines starting with '>').
+   * This is needed for signed messages that may contain quoted inner signatures.
+   */
+  private static findNonQuotedEndMarker(text: string, startIndex: number, endMarker: string): number {
+    let searchFrom = startIndex;
+    // eslint-disable-next-line no-constant-condition
+    while (true) {
+      const endIndex = text.indexOf(endMarker, searchFrom);
+      if (endIndex === -1) {
+        return -1; // No end marker found
+      }
+      // Find the start of the line containing this end marker
+      const lastLf = text.lastIndexOf('\n', endIndex - 1);
+      const lastCr = text.lastIndexOf('\r', endIndex - 1);
+      const lineStart = Math.max(lastLf, lastCr) + 1;
+      const linePrefix = text.substring(lineStart, endIndex);
+      // Check if line prefix contains quote markers (ignoring whitespace)
+      // A quoted line has '>' as the first non-whitespace character or after other '>'
+      const isQuoted = /^\s*>/.test(linePrefix);
+      if (!isQuoted) {
+        return endIndex; // Found a non-quoted end marker
+      }
+      // Continue searching after this occurrence
+      searchFrom = endIndex + endMarker.length;
+    }
+  }
+
   private static detectBlockNext(origText: string, startAt: number, completeOnly?: boolean) {
     const armorHdrTypes = Object.keys(PgpArmor.ARMOR_HEADER_DICT) as ReplaceableMsgBlockType[];
     const result: { found: MsgBlock[]; continueAt?: number } = { found: [] as MsgBlock[] };
@@ -190,7 +218,13 @@ export class MsgBlockParser {
             let endIndex = -1;
             let foundBlockEndHeaderLength = 0;
             if (typeof blockHeaderDef.end === 'string') {
-              endIndex = origText.indexOf(blockHeaderDef.end, begin + blockHeaderDef.begin.length);
+              // For signed messages, we need to find the end marker that is NOT quoted
+              // (i.e., not on a line starting with '>'). This handles nested quoted signatures.
+              if (armorHdrType === 'signedMsg') {
+                endIndex = MsgBlockParser.findNonQuotedEndMarker(origText, begin + blockHeaderDef.begin.length, blockHeaderDef.end);
+              } else {
+                endIndex = origText.indexOf(blockHeaderDef.end, begin + blockHeaderDef.begin.length);
+              }
               foundBlockEndHeaderLength = blockHeaderDef.end.length;
             } else {
               // regexp
diff --git a/test/source/tests/unit-node.ts b/test/source/tests/unit-node.ts
index cb246849a14..ff84049154b 100644
--- a/test/source/tests/unit-node.ts
+++ b/test/source/tests/unit-node.ts
@@ -224,6 +224,41 @@ Something wrong with this key`),
       t.pass();
     });
 
+    test(`[unit][MsgBlockParser.detectBlocks] correctly handles nested quoted signed messages`, async t => {
+      // This tests the fix for the bug where a signed message containing a quoted signed message
+      // would cause "Misformed armored text" error. The parser should find the correct (outer,
+      // non-quoted) END PGP SIGNATURE marker instead of the quoted inner one.
+      const nestedSignedMessage = `-----BEGIN PGP SIGNED MESSAGE-----
+Hash: SHA512
+
+This is the outer message.
+
+On 2026-01-15, someone@example.com wrote:
+> -----BEGIN PGP SIGNED MESSAGE-----
+> Hash: SHA512
+>
+> This is the quoted inner message.
+>
+> -----BEGIN PGP SIGNATURE-----
+> quotedSignatureData
+> -----END PGP SIGNATURE-----
+
+-----BEGIN PGP SIGNATURE-----
+outerSignatureData
+-----END PGP SIGNATURE-----`;
+
+      const { blocks } = MsgBlockParser.detectBlocks(nestedSignedMessage);
+      expect(blocks).to.have.length(1);
+      expect(blocks[0].type).to.equal('signedMsg');
+      // The block should contain the entire message including the quoted inner signature
+      expect(blocks[0].content).to.include('outerSignatureData');
+      expect(blocks[0].content).to.include('quotedSignatureData');
+      expect(blocks[0].content).to.include('-----BEGIN PGP SIGNED MESSAGE-----');
+      // Verify it ends with the outer signature, not the quoted one
+      expect(blocks[0].content).to.match(/outerSignatureData\n-----END PGP SIGNATURE-----$/);
+      t.pass();
+    });
+
     test(`[unit][PgpKey.usableForEncryptionButExpired] recognizes usable expired key`, async t => {
       const expiredKey = await KeyUtil.parse(testConstants.expiredPrv);
       expect(expiredKey.expiration).to.equal(1567605343000);