diff --git a/includes/ApiDiscussionToolsEdit.php b/includes/ApiDiscussionToolsEdit.php
index 6d3bb7339..2e3ba7bc8 100644
--- a/includes/ApiDiscussionToolsEdit.php
+++ b/includes/ApiDiscussionToolsEdit.php
@@ -106,9 +106,8 @@ class ApiDiscussionToolsEdit extends ApiBase {
 				$html = $params['html'];
 
 				if ( $wikitext !== null ) {
-					$wikitext = CommentUtils::htmlTrim( $wikitext );
 					if ( $signature !== null ) {
-						$wikitext .= $signature;
+						$wikitext = CommentModifier::appendSignatureWikitext( $wikitext, $signature );
 					}
 				} else {
 					$doc = DOMUtils::parseHTML( '' );
diff --git a/includes/ApiDiscussionToolsTrait.php b/includes/ApiDiscussionToolsTrait.php
index 71c251de1..b95e7548f 100644
--- a/includes/ApiDiscussionToolsTrait.php
+++ b/includes/ApiDiscussionToolsTrait.php
@@ -60,9 +60,8 @@ trait ApiDiscussionToolsTrait {
 		switch ( $type ) {
 			case 'topic':
 				if ( $wikitext !== null ) {
-					$wikitext = CommentUtils::htmlTrim( $wikitext );
 					if ( $signature !== null ) {
-						$wikitext .= $signature;
+						$wikitext = CommentModifier::appendSignatureWikitext( $wikitext, $signature );
 					}
 				} else {
 					$doc = DOMUtils::parseHTML( '' );
diff --git a/includes/CommentModifier.php b/includes/CommentModifier.php
index dfe00c576..5f231d1a0 100644
--- a/includes/CommentModifier.php
+++ b/includes/CommentModifier.php
@@ -446,9 +446,24 @@ class CommentModifier {
 	public static function appendSignature( DocumentFragment $container, string $signature ): void {
 		$doc = $container->ownerDocument;
 
-		// If the last node isn't a paragraph (e.g. it's a list created in visual mode), then
-		// add another paragraph to contain the signature.
-		if ( !$container->lastChild || strtolower( $container->lastChild->nodeName ) !== 'p' ) {
+		// If the last node isn't a paragraph (e.g. it's a list created in visual mode),
+		// or looks like a list item created in wikitext mode (T263217),
+		// then add another paragraph to contain the signature.
+		$wrapperNode = $container->lastChild;
+		if (
+			!( $wrapperNode instanceof Element ) ||
+			strtolower( $wrapperNode->tagName ) !== 'p' ||
+			(
+				// This would be easier to check in prepareWikitextReply(), but that would result
+				// in an empty list item being added at the end if we don't need to add a signature.
+				( $wtNode = $wrapperNode->lastChild ) &&
+				$wtNode instanceof Element &&
+				( $dataMw = json_decode( $wtNode->getAttribute( 'data-mw' ) ?? '', true ) ) &&
+				( $wikitextLine = $dataMw['parts'][0] ?? null ) &&
+				is_string( $wikitextLine ) &&
+				in_array( $wikitextLine[0], [ '*', '#', ':', ';' ] )
+			)
+		) {
 			$container->appendChild( $doc->createElement( 'p' ) );
 		}
 		// If the last node is empty, trim the signature to prevent leading whitespace triggering
@@ -465,6 +480,29 @@ class CommentModifier {
 		);
 	}
 
+	/**
+	 * Append a user signature to the comment in the provided wikitext.
+	 *
+	 * @param string $wikitext
+	 * @param string $signature
+	 * @return string
+	 */
+	public static function appendSignatureWikitext( string $wikitext, string $signature ): string {
+		$wikitext = CommentUtils::htmlTrim( $wikitext );
+
+		$lines = explode( "\n", $wikitext );
+		$lastLine = end( $lines );
+
+		// If last line looks like a list item, add an empty line afterwards for the signature (T263217)
+		if ( $lastLine && in_array( $lastLine[0], [ '*', '#', ':', ';' ] ) ) {
+			$wikitext .= "\n";
+			// Trim the signature to prevent leading whitespace triggering preformatted text (T269188, T276612)
+			$signature = ltrim( $signature, ' ' );
+		}
+
+		return $wikitext . $signature;
+	}
+
 	/**
 	 * Add a reply to a specific comment
 	 *
diff --git a/tests/cases/appendSignature.json b/tests/cases/appendSignature.json
index cdd6ce7cf..ddea3cdfa 100644
--- a/tests/cases/appendSignature.json
+++ b/tests/cases/appendSignature.json
@@ -4,11 +4,21 @@
 		"html": "<p>Foo bar</p>",
 		"expected": "<p>Foo bar<span typeof=\"mw:Transclusion\" data-mw=\"{&quot;parts&quot;:[&quot; ~~~~&quot;]}\"></span></p>"
 	},
+	{
+		"msg": "Simple message (from wikitext mode)",
+		"html": "<p><span typeof=\"mw:Transclusion\" data-mw=\"{&quot;parts&quot;:[&quot;Foo bar&quot;]}\"></span></p>",
+		"expected": "<p><span typeof=\"mw:Transclusion\" data-mw=\"{&quot;parts&quot;:[&quot;Foo bar&quot;]}\"></span><span typeof=\"mw:Transclusion\" data-mw=\"{&quot;parts&quot;:[&quot; ~~~~&quot;]}\"></span></p>"
+	},
 	{
 		"msg": "List",
 		"html": "<p>Foo bar</p><ul><li>A</li><li>B</li></ul>",
 		"expected": "<p>Foo bar</p><ul><li>A</li><li>B</li></ul><p><span typeof=\"mw:Transclusion\" data-mw=\"{&quot;parts&quot;:[&quot;~~~~&quot;]}\"></span></p>"
 	},
+	{
+		"msg": "List (from wikitext mode)",
+		"html": "<p><span typeof=\"mw:Transclusion\" data-mw=\"{&quot;parts&quot;:[&quot;Foo bar&quot;]}\"></span></p><p><span typeof=\"mw:Transclusion\" data-mw=\"{&quot;parts&quot;:[&quot;*A&quot;]}\"></span></p><p><span typeof=\"mw:Transclusion\" data-mw=\"{&quot;parts&quot;:[&quot;*B&quot;]}\"></span></p>",
+		"expected": "<p><span typeof=\"mw:Transclusion\" data-mw=\"{&quot;parts&quot;:[&quot;Foo bar&quot;]}\"></span></p><p><span typeof=\"mw:Transclusion\" data-mw=\"{&quot;parts&quot;:[&quot;*A&quot;]}\"></span></p><p><span typeof=\"mw:Transclusion\" data-mw=\"{&quot;parts&quot;:[&quot;*B&quot;]}\"></span></p><p><span typeof=\"mw:Transclusion\" data-mw=\"{&quot;parts&quot;:[&quot;~~~~&quot;]}\"></span></p>"
+	},
 	{
 		"msg": "Empty trailing paragraph",
 		"html": "<p>Foo bar</p><p></p>",
diff --git a/tests/phpunit/CommentModifierTest.php b/tests/phpunit/CommentModifierTest.php
index 2e1027604..bb80b23c6 100644
--- a/tests/phpunit/CommentModifierTest.php
+++ b/tests/phpunit/CommentModifierTest.php
@@ -147,6 +147,22 @@ class CommentModifierTest extends IntegrationTestCase {
 		return static::getJson( '../cases/appendSignature.json' );
 	}
 
+	/**
+	 * @covers ::appendSignatureWikitext
+	 */
+	public function testAppendSignatureWikitext(): void {
+		static::assertEquals(
+			'Foo bar ~~~~',
+			CommentModifier::appendSignatureWikitext( 'Foo bar', ' ~~~~' ),
+			'Simple message'
+		);
+		static::assertEquals(
+			"Foo bar\n*A\n*B\n~~~~",
+			CommentModifier::appendSignatureWikitext( "Foo bar\n*A\n*B", ' ~~~~' ),
+			'List'
+		);
+	}
+
 	/**
 	 * @dataProvider provideSanitizeWikitextLinebreaks
 	 * @covers ::sanitizeWikitextLinebreaks