diff --git a/includes/CommentParser.php b/includes/CommentParser.php
index d760b3c7d..11476541f 100644
--- a/includes/CommentParser.php
+++ b/includes/CommentParser.php
@@ -799,6 +799,19 @@ class CommentParser {
 		return $this->commentItems;
 	}
 
+	/**
+	 * Get all discussion comments (and headings) within a DOM subtree, grouped by item names.
+	 *
+	 * @return ThreadItem[][] Array where keys are thread item names, values are nonempty arrays of
+	 *     thread items
+	 */
+	public function getThreadItemsByName(): array {
+		if ( !$this->threadItems ) {
+			$this->buildThreads();
+		}
+		return $this->threadItemsByName;
+	}
+
 	/**
 	 * Find ThreadItems by their name
 	 *
diff --git a/includes/Notifications/EventDispatcher.php b/includes/Notifications/EventDispatcher.php
index 5fce9eb3e..899e34693 100644
--- a/includes/Notifications/EventDispatcher.php
+++ b/includes/Notifications/EventDispatcher.php
@@ -13,10 +13,12 @@ use EchoEvent;
 use Error;
 use IDBAccessObject;
 use Iterator;
+use MediaWiki\Extension\DiscussionTools\CommentItem;
 use MediaWiki\Extension\DiscussionTools\CommentParser;
 use MediaWiki\Extension\DiscussionTools\HeadingItem;
 use MediaWiki\Extension\DiscussionTools\Hooks\HookUtils;
 use MediaWiki\Extension\DiscussionTools\SubscriptionItem;
+use MediaWiki\Extension\DiscussionTools\ThreadItem;
 use MediaWiki\MediaWikiServices;
 use MediaWiki\Page\PageIdentity;
 use MediaWiki\Revision\RevisionRecord;
@@ -103,6 +105,27 @@ class EventDispatcher {
 		self::generateEventsFromParsers( $events, $oldParser, $newParser, $newRevRecord, $title, $user );
 	}
 
+	/**
+	 * For each top-level heading, get a list of comments in the thread grouped by names, then IDs.
+	 * (Compare by name first, as ID could be changed by a parent comment being moved/deleted.)
+	 *
+	 * @param ThreadItem[] $items
+	 * @return CommentItem[][][]
+	 */
+	private static function groupCommentsByThreadAndName( array $items ): array {
+		$comments = [];
+		$threadName = null;
+		foreach ( $items as $item ) {
+			if ( $item instanceof HeadingItem && ( $item->getHeadingLevel() <= 2 || $item->isPlaceholderHeading() ) ) {
+				$threadName = $item->getName();
+			} elseif ( $item instanceof CommentItem ) {
+				Assert::invariant( $threadName !== null, 'Comments are always preceded by headings' );
+				$comments[ $threadName ][ $item->getName() ][ $item->getId() ] = $item;
+			}
+		}
+		return $comments;
+	}
+
 	/**
 	 * Helper for generateEventsForRevision(), separated out for easier testing.
 	 *
@@ -121,16 +144,39 @@ class EventDispatcher {
 		PageIdentity $title,
 		UserIdentity $user
 	) {
-		$newComments = [];
-		foreach ( $newParser->getCommentItems() as $newComment ) {
-			if (
-				$newComment->getAuthor() === $user->getName() &&
-				// Compare comments by name, as ID could be changed by a parent comment
-				// being moved/deleted. The downside is that multiple replies within the
-				// same minute will only fire one notification.
-				count( $oldParser->findCommentsByName( $newComment->getName() ) ) === 0
-			) {
-				$newComments[] = $newComment;
+		$newComments = self::groupCommentsByThreadAndName( $newParser->getThreadItems() );
+		$oldComments = self::groupCommentsByThreadAndName( $oldParser->getThreadItems() );
+		$addedComments = [];
+
+		foreach ( $newComments as $threadName => $threadNewComments ) {
+			foreach ( $threadNewComments as $commentName => $nameNewComments ) {
+				// Usually, there will be 0 or 1 $nameNewComments, and 0 $nameOldComments,
+				// and $addedCount will be 0 or 1.
+				//
+				// But when multiple replies are added in one edit, or in multiple edits within the same
+				// minute, there may be more, and the complex logic below tries to make the best guess
+				// as to which comments are actually new. See the 'multiple' and 'sametime' test cases.
+				//
+				$nameOldComments = $oldComments[ $threadName ][ $commentName ] ?? [];
+				$addedCount = count( $nameNewComments ) - count( $nameOldComments );
+
+				if ( $addedCount > 0 ) {
+					// For any name that occurs more times in new than old, report that many new comments,
+					// preferring IDs that did not occur in old, then preferring comments lower in the thread.
+					foreach ( array_reverse( $nameNewComments ) as $commentId => $newComment ) {
+						if ( $addedCount > 0 && !isset( $nameOldComments[ $commentId ] ) ) {
+							$addedComments[] = $newComment;
+							$addedCount--;
+						}
+					}
+					foreach ( array_reverse( $nameNewComments ) as $commentId => $newComment ) {
+						if ( $addedCount > 0 ) {
+							$addedComments[] = $newComment;
+							$addedCount--;
+						}
+					}
+					Assert::postcondition( $addedCount === 0, 'Reported expected number of comments' );
+				}
 			}
 		}
 
@@ -142,7 +188,12 @@ class EventDispatcher {
 			}
 		}
 
-		foreach ( $newComments as $newComment ) {
+		foreach ( $addedComments as $newComment ) {
+			// Ignore comments by other users, e.g. in case of reverts or a discussion being moved.
+			// TODO: But what about someone signing another's comment?
+			if ( $newComment->getAuthor() !== $user->getName() ) {
+				continue;
+			}
 			$heading = $newComment->getHeading();
 			// Find a level 2 heading, because the interface doesn't allow subscribing to other headings.
 			// (T286736)
diff --git a/tests/cases/EventDispatcher/sametime/rev3-case1.json b/tests/cases/EventDispatcher/sametime/rev3-case1.json
index fe51488c7..4cf0c11e1 100644
--- a/tests/cases/EventDispatcher/sametime/rev3-case1.json
+++ b/tests/cases/EventDispatcher/sametime/rev3-case1.json
@@ -1 +1,16 @@
-[]
+[
+	{
+		"type": "dt-subscribed-new-comment",
+		"title": {},
+		"extra": {
+			"subscribed-comment-name": "h-X-2020-01-01T00:01:00.000Z",
+			"comment-id": "c-Z-2020-01-01T00:03:00.000Z-X-2020-01-01T00:01:00.000Z",
+			"comment-name": "c-Z-2020-01-01T00:03:00.000Z",
+			"content": "F.",
+			"section-title": "A",
+			"revid": null,
+			"mentioned-users": []
+		},
+		"agent": {}
+	}
+]
diff --git a/tests/cases/EventDispatcher/sametime/rev3-case2.json b/tests/cases/EventDispatcher/sametime/rev3-case2.json
index fe51488c7..4ab86183d 100644
--- a/tests/cases/EventDispatcher/sametime/rev3-case2.json
+++ b/tests/cases/EventDispatcher/sametime/rev3-case2.json
@@ -1 +1,16 @@
-[]
+[
+	{
+		"type": "dt-subscribed-new-comment",
+		"title": {},
+		"extra": {
+			"subscribed-comment-name": "h-Y-2020-01-01T00:02:00.000Z",
+			"comment-id": "c-Z-2020-01-01T00:03:00.000Z-Y-2020-01-01T00:02:00.000Z-1",
+			"comment-name": "c-Z-2020-01-01T00:03:00.000Z",
+			"content": "F.",
+			"section-title": "C",
+			"revid": null,
+			"mentioned-users": []
+		},
+		"agent": {}
+	}
+]
diff --git a/tests/cases/EventDispatcher/sametime/rev3-case3.json b/tests/cases/EventDispatcher/sametime/rev3-case3.json
index fe51488c7..c81050a55 100644
--- a/tests/cases/EventDispatcher/sametime/rev3-case3.json
+++ b/tests/cases/EventDispatcher/sametime/rev3-case3.json
@@ -1 +1,16 @@
-[]
+[
+	{
+		"type": "dt-subscribed-new-comment",
+		"title": {},
+		"extra": {
+			"subscribed-comment-name": "h-X-2020-01-01T00:01:00.000Z",
+			"comment-id": "c-Z-2020-01-01T00:03:00.000Z-X-2020-01-01T00:01:00.000Z",
+			"comment-name": "c-Z-2020-01-01T00:03:00.000Z",
+			"content": "E.",
+			"section-title": "A",
+			"revid": null,
+			"mentioned-users": []
+		},
+		"agent": {}
+	}
+]
diff --git a/tests/cases/EventDispatcher/sametime/rev3-case5.json b/tests/cases/EventDispatcher/sametime/rev3-case5.json
index fe51488c7..ce6e2fc17 100644
--- a/tests/cases/EventDispatcher/sametime/rev3-case5.json
+++ b/tests/cases/EventDispatcher/sametime/rev3-case5.json
@@ -1 +1,16 @@
-[]
+[
+	{
+		"type": "dt-subscribed-new-comment",
+		"title": {},
+		"extra": {
+			"subscribed-comment-name": "h-Y-2020-01-01T00:02:00.000Z",
+			"comment-id": "c-Z-2020-01-01T00:03:00.000Z-Y-2020-01-01T00:02:00.000Z-1",
+			"comment-name": "c-Z-2020-01-01T00:03:00.000Z",
+			"content": "E.",
+			"section-title": "C",
+			"revid": null,
+			"mentioned-users": []
+		},
+		"agent": {}
+	}
+]
diff --git a/tests/cases/EventDispatcher/sametime/rev3b-case7.json b/tests/cases/EventDispatcher/sametime/rev3b-case7.json
index fe51488c7..6c5c24b00 100644
--- a/tests/cases/EventDispatcher/sametime/rev3b-case7.json
+++ b/tests/cases/EventDispatcher/sametime/rev3b-case7.json
@@ -1 +1,16 @@
-[]
+[
+	{
+		"type": "dt-subscribed-new-comment",
+		"title": {},
+		"extra": {
+			"subscribed-comment-name": "h-Y-2020-01-01T00:02:00.000Z",
+			"comment-id": "c-Z-2020-01-01T00:05:00.000Z-X-2020-01-01T00:03:00.000Z",
+			"comment-name": "c-Z-2020-01-01T00:05:00.000Z",
+			"content": "H.",
+			"section-title": "C",
+			"revid": null,
+			"mentioned-users": []
+		},
+		"agent": {}
+	}
+]