Index: src/wp-includes/js/tinymce/skins/wordpress/wp-content.css
===================================================================
--- src/wp-includes/js/tinymce/skins/wordpress/wp-content.css	(revision 31360)
+++ src/wp-includes/js/tinymce/skins/wordpress/wp-content.css	(working copy)
@@ -68,6 +68,11 @@
 	background: transparent;
 }
 
+img,
+.wp-caption {
+	max-width: 100%;
+}
+
 .aligncenter,
 dl.aligncenter,
 .html5-captions .wp-caption.aligncenter {
@@ -125,6 +130,15 @@
 	margin: 0;
 }
 
+/* iOS does not obey max-width if width is set. */
+.ios .wp-caption {
+	width: auto !important;
+}
+
+.ios .wp-caption.aligncenter {
+	text-align: center;
+}
+
 /* Remove blue highlighting of selected images in WebKit */
 img::selection {
 	background-color: transparent;