diff --git a/workflow/engine/config/schema.xml b/workflow/engine/config/schema.xml
index 943d3deb7..5dcfcdb81 100644
--- a/workflow/engine/config/schema.xml
+++ b/workflow/engine/config/schema.xml
@@ -3198,6 +3198,9 @@
         <column name="CATEGORY_PARENT" type="VARCHAR" size="32" required="true" default="0"/>
         <column name="CATEGORY_NAME" type="VARCHAR" size="100" required="true" default=""/>
         <column name="CATEGORY_ICON" type="VARCHAR" size="100" default=""/>
+        <unique name="INDEX_CATEGORY_ID">
+            <unique-column name="CATEGORY_ID"/>
+        </unique>
     </table>
     <table name="APP_NOTES">
         <vendor type="mysql">
diff --git a/workflow/engine/data/mysql/schema.sql b/workflow/engine/data/mysql/schema.sql
index e94cd7b69..d815725b9 100644
--- a/workflow/engine/data/mysql/schema.sql
+++ b/workflow/engine/data/mysql/schema.sql
@@ -1553,7 +1553,8 @@ CREATE TABLE `PROCESS_CATEGORY`
 	`CATEGORY_PARENT` VARCHAR(32) default '0' NOT NULL,
 	`CATEGORY_NAME` VARCHAR(100) default '' NOT NULL,
 	`CATEGORY_ICON` VARCHAR(100) default '',
-	PRIMARY KEY (`CATEGORY_UID`)
+	PRIMARY KEY (`CATEGORY_UID`),
+	UNIQUE KEY `INDEX_CATEGORY_ID` (`CATEGORY_ID`)
 )ENGINE=InnoDB  DEFAULT CHARSET='utf8' COMMENT='Calendar Holidays';
 #-----------------------------------------------------------------------------
 #-- APP_NOTES