diff --git a/src/wp-includes/html-api/class-wp-html-tag-processor.php b/src/wp-includes/html-api/class-wp-html-tag-processor.php
index 95216b08a1988..11a0daa4b26f4 100644
--- a/src/wp-includes/html-api/class-wp-html-tag-processor.php
+++ b/src/wp-includes/html-api/class-wp-html-tag-processor.php
@@ -4009,7 +4009,13 @@ private function matches(): bool {
 		}
 
 		// Does the tag name match the requested tag name in a case-insensitive manner?
-		if ( isset( $this->sought_tag_name ) && 0 !== substr_compare( $this->html, $this->sought_tag_name, $this->tag_name_starts_at, $this->tag_name_length, true ) ) {
+		if (
+			isset( $this->sought_tag_name ) &&
+			(
+				strlen( $this->sought_tag_name ) !== $this->tag_name_length ||
+				0 !== substr_compare( $this->html, $this->sought_tag_name, $this->tag_name_starts_at, $this->tag_name_length, true )
+			)
+		) {
 			return false;
 		}
 
diff --git a/tests/phpunit/tests/html-api/wpHtmlTagProcessor.php b/tests/phpunit/tests/html-api/wpHtmlTagProcessor.php
index b9c6817988032..908e286a8fb21 100644
--- a/tests/phpunit/tests/html-api/wpHtmlTagProcessor.php
+++ b/tests/phpunit/tests/html-api/wpHtmlTagProcessor.php
@@ -601,6 +601,31 @@ public function test_next_tag_should_return_false_for_a_non_existing_tag() {
 		$this->assertFalse( $processor->next_tag( 'p' ), 'Querying a non-existing tag did not return false' );
 	}
 
+	/**
+	 * @ticket 61545
+	 */
+	public function test_next_tag_should_not_match_on_substrings_of_a_requested_tag() {
+		$processor = new WP_HTML_Tag_Processor( '<p><pic><picture>' );
+
+		$this->assertTrue(
+			$processor->next_tag( 'PICTURE' ),
+			'Failed to find a tag when requested: check test setup.'
+		);
+
+		$this->assertSame(
+			'PICTURE',
+			$processor->get_tag(),
+			'Should have skipped past substring tag matches, directly finding the PICTURE element.'
+		);
+
+		$processor = new WP_HTML_Tag_Processor( '<p><pic>' );
+
+		$this->assertFalse(
+			$processor->next_tag( 'PICTURE' ),
+			"Should not have found any PICTURE element, but found '{$processor->get_token_name()}' instead."
+		);
+	}
+
 	/**
 	 * @ticket 59209
 	 *