diff --git a/src/java/com/threerings/parlor/data/ParlorCodes.java b/src/java/com/threerings/parlor/data/ParlorCodes.java
index 2d08dc66..fd588b76 100644
--- a/src/java/com/threerings/parlor/data/ParlorCodes.java
+++ b/src/java/com/threerings/parlor/data/ParlorCodes.java
@@ -55,7 +55,11 @@ public interface ParlorCodes extends InvocationCodes
      * occupied. */
     public static final String TABLE_POSITION_OCCUPIED = "m.table_position_occupied";
 
-    /** An error code returned when a user requests to leave a table that
-     * they were not sitting at in the first place. */
+    /** An error code returned when a user requests to creat or join a table but they're already
+     * sitting at another table. */
+    public static final String ALREADY_AT_TABLE = "m.already_at_table";
+
+    /** An error code returned when a user requests to leave a table that they were not sitting at
+     * in the first place. */
     public static final String NOT_AT_TABLE = "m.not_at_table";
 }
diff --git a/src/java/com/threerings/parlor/server/TableManager.java b/src/java/com/threerings/parlor/server/TableManager.java
index 1b4d887b..9e96a7d7 100644
--- a/src/java/com/threerings/parlor/server/TableManager.java
+++ b/src/java/com/threerings/parlor/server/TableManager.java
@@ -116,6 +116,11 @@ public class TableManager
     public Table createTable (BodyObject creator, TableConfig tableConfig, GameConfig config)
         throws InvocationException
     {
+        // make sure the caller is not already in a table
+        if (_boidMap.containsKey(creator.getOid())) {
+            throw new InvocationException(ALREADY_AT_TABLE);
+        }
+
         // create a brand spanking new table
         Table table;
         try {
@@ -182,6 +187,11 @@ public class TableManager
     {
         BodyObject joiner = (BodyObject)caller;
 
+        // make sure the caller is not already in a table
+        if (_boidMap.containsKey(joiner.getOid())) {
+            throw new InvocationException(ALREADY_AT_TABLE);
+        }
+
         // look the table up
         Table table = _tables.get(tableId);
         if (table == null) {