diff --git a/src/wp-includes/formatting.php b/src/wp-includes/formatting.php
index 65fe00abf8..c5a1f53f7a 100644
--- a/src/wp-includes/formatting.php
+++ b/src/wp-includes/formatting.php
@@ -5496,27 +5496,24 @@ function sanitize_trackback_urls( $to_ping ) {
 }
 
 /**
- * Add slashes to a string or array of strings.
+ * Add slashes to a string or array of strings, in a recursive manner.
  *
  * This should be used when preparing data for core API that expects slashed data.
  * This should not be used to escape data going directly into an SQL query.
  *
  * @since 3.6.0
+ * @since 5.5.0 Leave a non-string value untouched.
  *
  * @param string|array $value String or array of strings to slash.
  * @return string|array Slashed $value
  */
 function wp_slash( $value ) {
 	if ( is_array( $value ) ) {
-		foreach ( $value as $k => $v ) {
-			if ( is_array( $v ) ) {
-				$value[ $k ] = wp_slash( $v );
-			} else {
-				$value[ $k ] = addslashes( $v );
-			}
-		}
-	} else {
-		$value = addslashes( $value );
+		$value = array_map( 'wp_slash', $value );
+	}
+
+	if ( is_string( $value ) ) {
+		return addslashes( $value );
 	}
 
 	return $value;
diff --git a/tests/phpunit/tests/formatting/StripSlashesDeep.php b/tests/phpunit/tests/formatting/StripSlashesDeep.php
index aaebf3be55..b27f6422e7 100644
--- a/tests/phpunit/tests/formatting/StripSlashesDeep.php
+++ b/tests/phpunit/tests/formatting/StripSlashesDeep.php
@@ -2,6 +2,7 @@
 
 /**
  * @group formatting
+ * @group slashes
  */
 class Tests_Formatting_StripSlashesDeep extends WP_UnitTestCase {
 	/**
diff --git a/tests/phpunit/tests/formatting/WPSlash.php b/tests/phpunit/tests/formatting/WPSlash.php
new file mode 100644
index 0000000000..bfe6759535
--- /dev/null
+++ b/tests/phpunit/tests/formatting/WPSlash.php
@@ -0,0 +1,103 @@
+<?php
+
+/**
+ * @group formatting
+ */
+class Tests_Formatting_WPSlash extends WP_UnitTestCase {
+
+	/**
+	 * @dataProvider data_wp_slash
+	 *
+	 * @ticket 42195
+	 *
+	 * @param string $value
+	 * @param string $expected
+	 */
+	public function test_wp_slash_with( $value, $expected ) {
+		$this->assertSame( $expected, wp_slash( $value ) );
+	}
+
+	/**
+	 * Data provider for test_wp_slash().
+	 *
+	 * @return array {
+	 *     @type array {
+	 *         @type mixed  $value    The value passed to wp_slash().
+	 *         @type string $expected The expected output of wp_slash().
+	 *     }
+	 * }
+	 */
+	public function data_wp_slash() {
+		return array(
+			array( 123, 123 ),
+			array( 123.4, 123.4 ),
+			array( true, true ),
+			array( false, false ),
+			array(
+				array(
+					'hello',
+					null,
+					'"string"',
+					125.41,
+				),
+				array(
+					'hello',
+					null,
+					'\"string\"',
+					125.41,
+				),
+			),
+			array( "first level 'string'", "first level \'string\'" ),
+		);
+	}
+
+	/**
+	 * @ticket 24106
+	 */
+	function test_adds_slashes() {
+		$old = "I can't see, isn't that it?";
+		$new = "I can\'t see, isn\'t that it?";
+		$this->assertEquals( $new, wp_slash( $old ) );
+		$this->assertEquals( "I can\\\\\'t see, isn\\\\\'t that it?", wp_slash( $new ) );
+		$this->assertEquals( array( 'a' => $new ), wp_slash( array( 'a' => $old ) ) ); // Keyed array
+		$this->assertEquals( array( $new ), wp_slash( array( $old ) ) ); // Non-keyed
+	}
+
+	/**
+	 * @ticket 24106
+	 */
+	function test_preserves_original_datatype() {
+
+		$this->assertEquals( true, wp_slash( true ) );
+		$this->assertEquals( false, wp_slash( false ) );
+		$this->assertEquals( 4, wp_slash( 4 ) );
+		$this->assertEquals( 'foo', wp_slash( 'foo' ) );
+		$arr      = array(
+			'a' => true,
+			'b' => false,
+			'c' => 4,
+			'd' => 'foo',
+		);
+		$arr['e'] = $arr; // Add a sub-array
+		$this->assertEquals( $arr, wp_slash( $arr ) ); // Keyed array
+		$this->assertEquals( array_values( $arr ), wp_slash( array_values( $arr ) ) ); // Non-keyed
+
+		$obj = new stdClass;
+		foreach ( $arr as $k => $v ) {
+			$obj->$k = $v;
+		}
+		$this->assertEquals( $obj, wp_slash( $obj ) );
+	}
+
+	/**
+	 * @ticket 24106
+	 */
+	function test_add_even_more_slashes() {
+		$old = 'single\\slash double\\\\slash triple\\\\\\slash';
+		$new = 'single\\\\slash double\\\\\\\\slash triple\\\\\\\\\\\\slash';
+		$this->assertEquals( $new, wp_slash( $old ) );
+		$this->assertEquals( array( 'a' => $new ), wp_slash( array( 'a' => $old ) ) ); // Keyed array
+		$this->assertEquals( array( $new ), wp_slash( array( $old ) ) ); // Non-keyed
+	}
+
+}