diff --git a/api.wordpress.org/public_html/dotorg/trac/pr/functions.php b/api.wordpress.org/public_html/dotorg/trac/pr/functions.php
index a2003c0aa4..78924963d6 100644
--- a/api.wordpress.org/public_html/dotorg/trac/pr/functions.php
+++ b/api.wordpress.org/public_html/dotorg/trac/pr/functions.php
@@ -497,6 +497,37 @@ function trac_comment_code_block( $fence ) {
 		$m['indent'] . '}}}';
 }
 
+/**
+ * Converts the ATX headings of one span to Trac headings.
+ *
+ * @param string $text A span of the pull request lying outside any fenced code block.
+ * @return string|false The span with its headings converted, or false if it cannot be built.
+ */
+function trac_comment_headings( $text ) {
+	$skipped = trac_comment_skipped();
+
+	// A heading is separated by whitespace alone; a `>` after its `=` run is text.
+	$space = str_replace( '>', '', $skipped );
+
+	$text = preg_replace( "~^{$skipped}*\K(?=={1,6}{$space})~mu", '!', $text );
+	if ( null === $text ) {
+		return false;
+	}
+
+	$text = preg_replace_callback(
+		'~^(?P<cite>[ \t]*>[ \t>]*)?[ \t]{0,3}(?P<hashes>\#{1,6})[ \t]+(?P<text>.+?)(?:[ \t]+\#+)?[ \t]*$~m',
+		function ( $m ) {
+			$level = str_repeat( '=', strlen( $m['hashes'] ) );
+			$cite  = '' === $m['cite'] ? '' : rtrim( $m['cite'] ) . ' ';
+
+			return "{$cite}{$level} {$m['text']} {$level}";
+		},
+		$text
+	);
+
+	return is_string( $text ) ? $text : false;
+}
+
 /**
  * Converts one span of pull request text to Trac wiki markup.
  *
@@ -642,6 +673,7 @@ function ( $m ) {
  * This:
  *  - Strips HTML comments
  *  - Converts code blocks
+ *  - Converts headings
  *  - Converts image embeds
  *  - Converts links
  *  - Converts tables
@@ -666,7 +698,14 @@ function format_github_content_for_trac_comment( $desc ) {
 	}
 
 	foreach ( $parts as $i => $part ) {
-		$part = ( $i % 2 ) ? trac_comment_code_block( $part ) : trac_comment_wiki_text( $part );
+		if ( $i % 2 ) {
+			$part = trac_comment_code_block( $part );
+		} else {
+			// A heading is a whole line, and only this split's spans begin and end where lines do.
+			$part = trac_comment_headings( $part );
+			$part = is_string( $part ) ? trac_comment_wiki_text( $part ) : false;
+		}
+
 		if ( false === $part ) {
 			return false;
 		}
diff --git a/api.wordpress.org/public_html/dotorg/trac/pr/tests/Trac_Comment_Heading_Test.php b/api.wordpress.org/public_html/dotorg/trac/pr/tests/Trac_Comment_Heading_Test.php
new file mode 100644
index 0000000000..1b781653d6
--- /dev/null
+++ b/api.wordpress.org/public_html/dotorg/trac/pr/tests/Trac_Comment_Heading_Test.php
@@ -0,0 +1,314 @@
+<?php
+/**
+ * Tests that Markdown headings reach Trac as Trac headings.
+ *
+ * Trac reads WikiCreole's `=`, not Markdown's `#`, so an unconverted heading
+ * renders as its own literal text. The reverse also holds: a body that opens a
+ * line with `=` writes a heading the pull request never asked for.
+ *
+ * @package trac-pr
+ */
+
+declare( strict_types = 1 );
+
+namespace WordPressdotorg\API\Trac\GithubPRs;
+
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Tests for the heading handling of the GitHub to Trac comment composer.
+ */
+class Trac_Comment_Heading_Test extends TestCase {
+
+	/**
+	 * Every Markdown heading level has a Trac heading of the same depth.
+	 *
+	 * @dataProvider data_heading_levels
+	 *
+	 * @param string $body   A pull request body.
+	 * @param string $expect The heading it must compose.
+	 * @return void
+	 */
+	public function test_a_heading_is_converted( string $body, string $expect ) {
+		$desc = format_github_content_for_trac_comment( $body );
+
+		$this->assertIsString( $desc );
+		$this->assertStringContainsString( $expect, $desc );
+	}
+
+	/**
+	 * Supplies one pull request heading per level.
+	 *
+	 * @return array Bodies and the headings they must compose.
+	 */
+	public function data_heading_levels(): array {
+		return array(
+			'level one'   => array( "# Summary\n\nText.\n", '= Summary =' ),
+			'level two'   => array( "## Summary\n\nText.\n", '== Summary ==' ),
+			'level three' => array( "### Summary\n\nText.\n", '=== Summary ===' ),
+			'level four'  => array( "#### Summary\n\nText.\n", '==== Summary ====' ),
+			'level five'  => array( "##### Summary\n\nText.\n", '===== Summary =====' ),
+			'level six'   => array( "###### Summary\n\nText.\n", '====== Summary ======' ),
+		);
+	}
+
+	/**
+	 * A seventh `#` is past Trac's deepest heading, so the line is left as text.
+	 *
+	 * @return void
+	 */
+	public function test_a_seventh_level_is_not_a_heading() {
+		$desc = format_github_content_for_trac_comment( "####### Summary\n\nText.\n" );
+
+		$this->assertIsString( $desc );
+		$this->assertStringContainsString( '####### Summary', $desc );
+	}
+
+	/**
+	 * Markdown's optional closing run belongs to the marker, not to the title.
+	 *
+	 * @return void
+	 */
+	public function test_a_closed_heading_keeps_only_its_title() {
+		$desc = format_github_content_for_trac_comment( "## Summary ##\n\nText.\n" );
+
+		$this->assertIsString( $desc );
+		$this->assertStringContainsString( '== Summary ==', $desc );
+		$this->assertStringNotContainsString( '## ', $desc );
+	}
+
+	/**
+	 * Up to three leading spaces are Markdown's, and Trac has no use for them.
+	 *
+	 * @return void
+	 */
+	public function test_an_indented_heading_is_converted() {
+		$desc = format_github_content_for_trac_comment( "Text.\n\n   ## Summary\n" );
+
+		$this->assertIsString( $desc );
+		$this->assertStringContainsString( "\n== Summary ==", $desc );
+	}
+
+	/**
+	 * A line that only looks like a heading must reach Trac as it was written.
+	 *
+	 * @dataProvider data_non_headings
+	 *
+	 * @param string $body A pull request body opening a line with `#`.
+	 * @return void
+	 */
+	public function test_a_hash_that_is_not_a_heading_is_left_alone( string $body ) {
+		$this->assertSame( trim( $body ), format_github_content_for_trac_comment( $body ) );
+	}
+
+	/**
+	 * Supplies the line-opening hashes that are not Markdown headings.
+	 *
+	 * @return array Bodies that must be composed unchanged.
+	 */
+	public function data_non_headings(): array {
+		return array(
+			'ticket reference' => array( "#65845 is the ticket.\n" ),
+			'no space'         => array( "#Summary\n" ),
+			'interpreter line' => array( "#!/bin/sh\n" ),
+			'empty heading'    => array( "## \n" ),
+			'four spaces'      => array( "Text.\n\n    ## Summary\n" ),
+		);
+	}
+
+	/**
+	 * Trac strips a citation's `>` before it reads the line, so a quote has headings too.
+	 *
+	 * @dataProvider data_cited_headings
+	 *
+	 * @param string $body   A pull request body quoting a heading.
+	 * @param string $expect The quoted line it must compose.
+	 * @return void
+	 */
+	public function test_a_cited_heading_keeps_its_citation( string $body, string $expect ) {
+		$desc = format_github_content_for_trac_comment( $body );
+
+		$this->assertIsString( $desc );
+		$this->assertStringContainsString( $expect, $desc );
+	}
+
+	/**
+	 * Supplies the quoted lines Trac reads as a heading.
+	 *
+	 * @return array Bodies and the quoted lines they must compose.
+	 */
+	public function data_cited_headings(): array {
+		return array(
+			'converted'        => array( "> ## Summary\n", '> == Summary ==' ),
+			'no space'         => array( ">## Summary\n", '> == Summary ==' ),
+			'nested'           => array( "> > ## Summary\n", '> > == Summary ==' ),
+			'escaped'          => array( "> == Summary\n", '> !== Summary' ),
+			'escaped nested'   => array( "> > == Summary\n", '> > !== Summary' ),
+			'escaped indented' => array( ">   == Summary\n", '>   !== Summary' ),
+		);
+	}
+
+	/**
+	 * A quotation deep enough to exhaust PCRE's stack must still reach the ticket.
+	 *
+	 * A pattern that repeats a group rather than naming a character class gives up on
+	 * a line like this, and a refused span takes the whole comment with it.
+	 *
+	 * @dataProvider data_deep_citations
+	 *
+	 * @param string $line   The line to quote, once the citation is prepended.
+	 * @param string $expect The end of the line it must compose.
+	 * @return void
+	 */
+	public function test_a_deep_citation_does_not_refuse_the_comment( string $line, string $expect ) {
+		// Two characters per level, within GitHub's 65536 character body.
+		$desc = format_github_content_for_trac_comment( str_repeat( '> ', 30000 ) . $line );
+
+		$this->assertIsString( $desc );
+		$this->assertStringEndsWith( $expect, $desc );
+	}
+
+	/**
+	 * Supplies the deeply quoted lines that must survive the composer.
+	 *
+	 * @return array Lines to quote and the endings they must compose.
+	 */
+	public function data_deep_citations(): array {
+		return array(
+			'converted' => array( "## Summary\n", '== Summary ==' ),
+			'escaped'   => array( "== Summary\n", '!== Summary' ),
+			'neither'   => array( "Summary\n", '> Summary' ),
+		);
+	}
+
+	/**
+	 * A heading's own inline code must stay inside the heading.
+	 *
+	 * The composer splits a span on its inline code, so a heading cut in half by a
+	 * backtick would otherwise close over the first piece alone.
+	 *
+	 * @return void
+	 */
+	public function test_a_heading_holding_inline_code_stays_one_heading() {
+		$desc = format_github_content_for_trac_comment( "## The `retention-days` key\n\nText.\n" );
+
+		$this->assertIsString( $desc );
+		$this->assertStringContainsString( '== The `retention-days` key ==', $desc );
+	}
+
+	/**
+	 * Inline code that opens a line is content, not a marker.
+	 *
+	 * @return void
+	 */
+	public function test_a_hash_inside_inline_code_is_not_a_heading() {
+		$desc = format_github_content_for_trac_comment( "Write `## Summary` for a heading.\n" );
+
+		$this->assertIsString( $desc );
+		$this->assertStringContainsString( '`## Summary`', $desc );
+	}
+
+	/**
+	 * A heading's links and images are converted with the rest of the prose.
+	 *
+	 * @return void
+	 */
+	public function test_a_heading_still_converts_its_links() {
+		$desc = format_github_content_for_trac_comment( "## See [the docs](https://example.org/doc)\n" );
+
+		$this->assertSame( '== See [https://example.org/doc the docs] ==', $desc );
+	}
+
+	/**
+	 * A fenced block's contents are code, so its hashes are not headings.
+	 *
+	 * @return void
+	 */
+	public function test_a_hash_inside_a_fence_is_not_a_heading() {
+		$desc = format_github_content_for_trac_comment( "Text.\n\n```sh\n## Summary\n```\n" );
+
+		$this->assertIsString( $desc );
+		$this->assertStringContainsString( "\n## Summary\n", $desc );
+		$this->assertStringNotContainsString( '== Summary ==', $desc );
+	}
+
+	/**
+	 * Trac's own heading marker is the composer's to write, not the body's.
+	 *
+	 * @dataProvider data_wiki_headings
+	 *
+	 * @param string $body   A pull request body opening a line with `=`.
+	 * @param string $expect The escaped line it must compose.
+	 * @return void
+	 */
+	public function test_a_wiki_heading_in_the_body_is_escaped( string $body, string $expect ) {
+		$desc = format_github_content_for_trac_comment( $body );
+
+		$this->assertIsString( $desc );
+		$this->assertStringContainsString( $expect, $desc );
+	}
+
+	/**
+	 * Supplies the line-opening `=` runs Trac would read as a heading.
+	 *
+	 * @return array Bodies and the escaped lines they must compose.
+	 */
+	public function data_wiki_headings(): array {
+		return array(
+			'bare'           => array( "== Summary\n", '!== Summary' ),
+			'closed'         => array( "== Summary ==\n", '!== Summary ==' ),
+			'indented'       => array( "Text.\n\n  = Summary =\n", "\n  !=" ),
+			'deepest'        => array( "====== Summary\n", '!====== Summary' ),
+			'tab spaced'     => array( "==\tSummary\n", "!==\tSummary" ),
+			// Trac steps over Python's whitespace, which is wider than PCRE's.
+			'no-break'       => array( "Text.\n\n\u{00A0}== Summary\n", "\u{00A0}!== Summary" ),
+			'en space'       => array( "Text.\n\n\u{2002}== Summary\n", "\u{2002}!== Summary" ),
+			'ideographic'    => array( "Text.\n\n\u{3000}== Summary\n", "\u{3000}!== Summary" ),
+			'unit separator' => array( "Text.\n\n\x1f== Summary\n", "\x1f!== Summary" ),
+			// The same class again, this time separating the marker from the title.
+			'no-break sep'   => array( "Text.\n\n==\u{00A0}Summary\n", "!==\u{00A0}Summary" ),
+			'en space sep'   => array( "Text.\n\n==\u{2002}Summary\n", "!==\u{2002}Summary" ),
+			'cited sep'      => array( "Text.\n\n> ==\u{00A0}Summary\n", "> !==\u{00A0}Summary" ),
+		);
+	}
+
+	/**
+	 * An `=` that opens no heading of Trac's is prose, and stays prose.
+	 *
+	 * @dataProvider data_inert_equals
+	 *
+	 * @param string $body A pull request body opening a line with `=`.
+	 * @return void
+	 */
+	public function test_an_inert_equals_is_left_alone( string $body ) {
+		$this->assertSame( trim( $body ), format_github_content_for_trac_comment( $body ) );
+	}
+
+	/**
+	 * Supplies the line-opening `=` runs Trac reads as text.
+	 *
+	 * @return array Bodies that must be composed unchanged.
+	 */
+	public function data_inert_equals(): array {
+		return array(
+			'no space' => array( "=Summary\n" ),
+			'citation' => array( "==> Not a heading.\n" ),
+			'too deep' => array( "======= Summary\n" ),
+			'arrow'    => array( "=> Returns the value.\n" ),
+		);
+	}
+
+	/**
+	 * A heading must not gain the escape written for the line above it.
+	 *
+	 * @return void
+	 */
+	public function test_an_escape_and_a_heading_can_share_a_body() {
+		$desc = format_github_content_for_trac_comment( "== Written\n\n## Composed\n" );
+
+		$this->assertIsString( $desc );
+		$this->assertStringContainsString( '!== Written', $desc );
+		$this->assertStringContainsString( '== Composed ==', $desc );
+		$this->assertStringNotContainsString( '!== Composed', $desc );
+	}
+}
diff --git a/api.wordpress.org/public_html/dotorg/trac/pr/webhook.php b/api.wordpress.org/public_html/dotorg/trac/pr/webhook.php
index 7e705b9709..fe0da1fe8c 100644
--- a/api.wordpress.org/public_html/dotorg/trac/pr/webhook.php
+++ b/api.wordpress.org/public_html/dotorg/trac/pr/webhook.php
@@ -73,7 +73,7 @@ function verify_signature() {
 			foreach ( $existing_refs as $ref ) {
 				if (
 					$ref->trac === $pr_data->trac_ticket[0] &&
-					$ref->ticket === $pr_data->trac_ticket[1]
+					(int) $ref->ticket === (int) $pr_data->trac_ticket[1]
 				) {
 					$matched_existing_ref = true;
 				}
@@ -85,11 +85,14 @@ function verify_signature() {
 		unset( $_pr_data_no_ticket->trac_ticket, $_pr_data_no_ticket->body );
 
 		// Step 3. If not in DB, or $pr_data->trac_ticket isn't yet in the DB, add a new row of it.
+		$user_id = 0;
+		$new_ref = false;
+
 		if ( $pr_data->trac_ticket && ( ! $existing_refs || ! $matched_existing_ref ) ) {
 
 			$user_id = (int) find_wporg_user_by_github( $pr_data->user->name, 'ID' );
 
-			$wpdb->insert(
+			$new_ref = (bool) $wpdb->insert(
 				'trac_github_prs',
 				[
 					'created'      => gmdate( 'Y-m-d H:i:s', strtotime( $pr_data->created_at ) ),
@@ -102,6 +105,10 @@ function verify_signature() {
 					'author'       => $user_id,
 				]
 			);
+		}
+
+		// Only the request whose row was added mentions the PR on the ticket.
+		if ( $new_ref ) {
 
 			// Add a mention to the Trac Ticket.
 			$trac = get_trac_instance( $pr_data->trac_ticket[0] );