Index: src/wp-includes/class-http.php
===================================================================
--- src/wp-includes/class-http.php	(revision 38700)
+++ src/wp-includes/class-http.php	(working copy)
@@ -361,6 +361,9 @@
 		// Work around a bug in Requests when the path starts with // See https://github.com/rmccue/Requests/issues/231
 		$url = preg_replace( '!^(\w+://[^/]+)//(.*)$!i', '$1/$2', $url );
 
+		// Avoid issues where mbstring.func_overload is enabled
+		mbstring_binary_safe_encoding();
+
 		try {
 			$requests_response = Requests::request( $url, $headers, $data, $type, $options );
 
@@ -375,6 +378,8 @@
 			$response = new WP_Error( 'http_request_failed', $e->getMessage() );
 		}
 
+		reset_mbstring_encoding();
+
 		/**
 		 * Fires after an HTTP API response is received and before the response is returned.
 		 *