Index: wp-content/themes/twentythirteen/style.css
===================================================================
--- wp-content/themes/twentythirteen/style.css	(revision 23649)
+++ wp-content/themes/twentythirteen/style.css	(working copy)
@@ -1523,10 +1523,19 @@
 .search .format-gallery .gallery-item img {
 	height: 100%;
 	max-height: 148px;
-	max-width: 1000%;
+	max-width: none;
 	width: auto;
 }
 
+.blog .format-gallery .gallery-item .portrait img, 
+.archive .format-gallery .gallery-item .portrait img, 
+.search .format-gallery .gallery-item .portrait img { 
+	height: auto; 
+	max-height: none; 
+	max-width: 148px; 
+	width: 100%; 
+}
+
 .blog .format-gallery .gallery-item:first-child,
 .archive .format-gallery .gallery-item:first-child,
 .search .format-gallery .gallery-item:first-child {
@@ -1540,6 +1549,13 @@
 	max-height: 300px;
 }
 
+.blog .format-gallery .gallery-item:first-child .portrait img,
+.archive .format-gallery .gallery-item:first-child .portrait img,
+.search .format-gallery .gallery-item:first-child .portrait img {
+	max-height: none;
+	max-width: 300px;
+}
+
 .blog .format-gallery .gallery-item .gallery-icon,
 .archive .format-gallery .gallery-item .gallery-icon,
 .search .format-gallery .gallery-item .gallery-icon {