diff --git a/src/wp-includes/functions.php b/src/wp-includes/functions.php
index f5002a45de1e8..80880c3121a0b 100644
--- a/src/wp-includes/functions.php
+++ b/src/wp-includes/functions.php
@@ -7679,7 +7679,7 @@ function get_tag_regex( $tag ) {
 	if ( empty( $tag ) ) {
 		return '';
 	}
-	return sprintf( '<%1$s[^<]*(?:>[\s\S]*<\/%1$s>|\s*\/>)', tag_escape( $tag ) );
+	return sprintf( '<%1$s[^<]*?(?:>[\s\S]*?<\/%1$s>|\s*\/>)', tag_escape( $tag ) );
 }
 
 /**
diff --git a/tests/phpunit/tests/functions/getTagRegex.php b/tests/phpunit/tests/functions/getTagRegex.php
new file mode 100644
index 0000000000000..8988de987548b
--- /dev/null
+++ b/tests/phpunit/tests/functions/getTagRegex.php
@@ -0,0 +1,95 @@
+<?php
+
+/**
+ * Tests for the get_tag_regex() function.
+ *
+ * @group functions
+ *
+ * @covers ::get_tag_regex
+ */
+class Tests_Functions_GetTagRegex extends WP_UnitTestCase {
+
+	/**
+	 * @ticket 26674
+	 *
+	 * @dataProvider data_get_tag_regex_matches
+	 *
+	 * @param string   $tag      Tag name to build the regex for.
+	 * @param string   $content  Content to match against.
+	 * @param string[] $expected Expected full matches, in order.
+	 */
+	public function test_get_tag_regex_matches( $tag, $content, $expected ) {
+		preg_match_all( '#' . get_tag_regex( $tag ) . '#', $content, $matches );
+		$this->assertSame( $expected, $matches[0] );
+	}
+
+	/**
+	 * Data provider.
+	 *
+	 * @return array[]
+	 */
+	public function data_get_tag_regex_matches() {
+		return array(
+			'a single tag with a body'                 => array(
+				'iframe',
+				'<iframe src="https://example.com/a"></iframe>',
+				array( '<iframe src="https://example.com/a"></iframe>' ),
+			),
+
+			// The regression: a greedy match ran from the first opening tag to
+			// the last closing tag, merging both embeds and the text between
+			// them into a single match. See #26674.
+			'two adjacent tags are matched separately' => array(
+				'iframe',
+				'<iframe src="https://example.com/a"></iframe> text <iframe src="https://example.com/b"></iframe>',
+				array(
+					'<iframe src="https://example.com/a"></iframe>',
+					'<iframe src="https://example.com/b"></iframe>',
+				),
+			),
+
+			// A self-closing void element (an iframe cannot self-close), matched
+			// both with and without the space before the slash (comment:16).
+			'a self-closing tag with a space'          => array(
+				'input',
+				'<input type="text" />',
+				array( '<input type="text" />' ),
+			),
+
+			'a self-closing tag without a space'       => array(
+				'input',
+				'<input type="text"/>',
+				array( '<input type="text"/>' ),
+			),
+
+			'a tag with a multiline body'              => array(
+				'video',
+				"<video>\n<source src=\"a.mp4\">\n</video>",
+				array( "<video>\n<source src=\"a.mp4\">\n</video>" ),
+			),
+
+			'no match when the tag is absent'          => array(
+				'iframe',
+				'<p>No embeds here.</p>',
+				array(),
+			),
+		);
+	}
+
+	/**
+	 * @ticket 26674
+	 */
+	public function test_get_tag_regex_returns_empty_string_for_empty_tag() {
+		$this->assertSame( '', get_tag_regex( '' ) );
+	}
+
+	/**
+	 * The tag name is passed through tag_escape(), so casing and invalid
+	 * characters do not change the generated pattern.
+	 *
+	 * @ticket 26674
+	 */
+	public function test_get_tag_regex_escapes_the_tag_name() {
+		$this->assertSame( get_tag_regex( 'iframe' ), get_tag_regex( 'IFRAME' ) );
+	}
+}