diff --git a/core/themes/seven/style.css b/core/themes/seven/style.css
index b298d1c..551dfd7 100644
--- a/core/themes/seven/style.css
+++ b/core/themes/seven/style.css
@@ -481,6 +481,12 @@ table th.active img {
   top: 3px;
   right: 3px; /* LTR */
 }
+/**
+ * Force browsers to calculate the width of a 'select all' TH element.
+ */
+table th.select-all {
+  width: 1px;
+}
 table td.active {
   background: #e9e9dd;
 }