diff --git a/src/wp-includes/formatting.php b/src/wp-includes/formatting.php
index 956e8290e2..50b43a5175 100644
--- a/src/wp-includes/formatting.php
+++ b/src/wp-includes/formatting.php
@@ -4883,7 +4883,11 @@ function sanitize_option( $option, $value ) {
 			break;
 
 		case 'blog_charset':
-			$value = preg_replace( '/[^a-zA-Z0-9_-]/', '', $value ); // Strips slashes.
+			if ( is_string( $value ) ) {
+				$value = preg_replace( '/[^a-zA-Z0-9_-]/', '', $value ); // Strips slashes.
+			} else {
+				$value = '';
+			}
 			break;
 
 		case 'blog_public':
@@ -4918,7 +4922,11 @@ function sanitize_option( $option, $value ) {
 			break;
 
 		case 'gmt_offset':
-			$value = preg_replace( '/[^0-9:.-]/', '', $value ); // Strips slashes.
+			if ( is_numeric( $value ) ) {
+				$value = preg_replace( '/[^0-9:.-]/', '', $value ); // Strips slashes.
+			} else {
+				$value = '';
+			}
 			break;
 
 		case 'siteurl':
diff --git a/tests/phpunit/tests/option/sanitizeOption.php b/tests/phpunit/tests/option/sanitizeOption.php
index e50cec0c62..38fdda1a21 100644
--- a/tests/phpunit/tests/option/sanitizeOption.php
+++ b/tests/phpunit/tests/option/sanitizeOption.php
@@ -36,6 +36,7 @@ class Tests_Option_SanitizeOption extends WP_UnitTestCase {
 			array( 'blogname', '&lt;i&gt;My Site&lt;/i&gt;', '<i>My Site</i>' ),
 			array( 'blog_charset', 'UTF-8', 'UTF-8' ),
 			array( 'blog_charset', 'charset', '">charset<"' ),
+			array( 'blog_charset', '', null ),
 			array( 'blog_public', 1, null ),
 			array( 'blog_public', 1, '1' ),
 			array( 'blog_public', -2, '-2' ),
@@ -45,6 +46,7 @@ class Tests_Option_SanitizeOption extends WP_UnitTestCase {
 			array( 'ping_sites', "http://www.example.com\nhttp://example.org", "www.example.com \n\texample.org\n\n" ),
 			array( 'gmt_offset', '0', 0 ),
 			array( 'gmt_offset', '1.5', '1.5' ),
+			array( 'gmt_offset', '', null ),
 			array( 'siteurl', 'http://example.org', 'http://example.org' ),
 			array( 'siteurl', 'http://example.org/subdir', 'http://example.org/subdir' ),
 			array( 'siteurl', get_option( 'siteurl' ), '' ),