diff --git a/wp-admin/includes/upgrade.php b/wp-admin/includes/upgrade.php
index a8b4c740a5..dde618ab02 100644
--- a/wp-admin/includes/upgrade.php
+++ b/wp-admin/includes/upgrade.php
@@ -1751,6 +1751,17 @@ function maybe_convert_table_to_utf8mb4( $table ) {
 		}
 	}
 
+	$table_details = $wpdb->get_row( "SHOW TABLE STATUS LIKE '$table'" );
+	if ( ! $table_details ) {
+		return false;
+	}
+
+	list( $table_charset ) = explode( '_', $table_details->Collation );
+	$table_charset = strtolower( $table_charset );
+	if ( 'utf8mb4' === $table_charset ) {
+		return true;
+	}
+
 	return $wpdb->query( "ALTER TABLE $table CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci" );
 }
 
diff --git a/wp-includes/version.php b/wp-includes/version.php
index d5fa32dad4..c35b6c709a 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -4,7 +4,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '4.3-alpha-32455';
+$wp_version = '4.3-alpha-32456';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.