diff -u b/core/modules/simpletest/simpletest.install b/core/modules/simpletest/simpletest.install
--- b/core/modules/simpletest/simpletest.install
+++ b/core/modules/simpletest/simpletest.install
@@ -110,6 +110,7 @@
       'test_class' => array(
         'type' => 'varchar',
         'length' => 255,
+        'is_ascii' => TRUE,
         'not null' => TRUE,
         'default' => '',
         'description' => 'The name of the class that created this message.',
diff -u b/core/modules/system/system.install b/core/modules/system/system.install
--- b/core/modules/system/system.install
+++ b/core/modules/system/system.install
@@ -929,6 +929,7 @@
       'value' => array(
         'description' => 'A value for the semaphore.',
         'type' => 'varchar',
+        'is_ascii' => TRUE,
         'length' => 255,
         'not null' => TRUE,
         'default' => ''