diff --git a/arangod/VocBase/barrier.c b/arangod/VocBase/barrier.c
index f640ec7a0b..8cd2d7f271 100644
--- a/arangod/VocBase/barrier.c
+++ b/arangod/VocBase/barrier.c
@@ -27,12 +27,57 @@
 
 #include "barrier.h"
 
+#include "BasicsC/logging.h"
 #include "VocBase/document-collection.h"
 
 // -----------------------------------------------------------------------------
 // --SECTION--                                                           BARRIER
 // -----------------------------------------------------------------------------
 
+// -----------------------------------------------------------------------------
+// --SECTION--                                                 private functions
+// -----------------------------------------------------------------------------
+
+////////////////////////////////////////////////////////////////////////////////
+/// @addtogroup VocBase
+/// @{
+////////////////////////////////////////////////////////////////////////////////
+
+////////////////////////////////////////////////////////////////////////////////
+/// @brief inserts the barrier element into the linked list of barrier elemnents
+/// of the collection
+////////////////////////////////////////////////////////////////////////////////
+  
+static void LinkBarrierElement (TRI_barrier_t* element, TRI_barrier_list_t* container) {
+  element->_container = container;
+
+  TRI_LockSpin(&container->_lock);
+
+  // empty list
+  if (container->_end == NULL) {
+    element->_next = NULL;
+    element->_prev = NULL;
+
+    container->_begin = element;
+    container->_end = element;
+  }
+
+  // add to the end
+  else {
+    element->_next = NULL;
+    element->_prev = container->_end;
+
+    container->_end->_next = element;
+    container->_end = element;
+  }
+  
+  TRI_UnlockSpin(&container->_lock);
+}
+
+////////////////////////////////////////////////////////////////////////////////
+/// @}
+////////////////////////////////////////////////////////////////////////////////
+
 // -----------------------------------------------------------------------------
 // --SECTION--                                      constructors and destructors
 // -----------------------------------------------------------------------------
@@ -66,14 +111,48 @@ void TRI_DestroyBarrierList (TRI_barrier_list_t* container) {
   ptr = container->_begin;
 
   while (ptr != NULL) {
-    next = ptr->_next;
     ptr->_container = NULL;
+    next = ptr->_next;
+
+    if (ptr->_type == TRI_BARRIER_COLLECTION_UNLOAD_CALLBACK ||
+        ptr->_type == TRI_BARRIER_COLLECTION_DROP_CALLBACK ||
+        ptr->_type == TRI_BARRIER_DATAFILE_CALLBACK) {
+      // free data still allocated in barrier elements
+      TRI_Free(TRI_UNKNOWN_MEM_ZONE, ptr);
+    }
+    else if (ptr->_type == TRI_BARRIER_ELEMENT) {
+      LOG_ERROR("logic error. shouldn't have barrier elements in barrierlist on unload");
+    }
+
     ptr = next;
   }
 
   TRI_DestroySpin(&container->_lock);
 }
 
+////////////////////////////////////////////////////////////////////////////////
+/// @brief check whether the barrier list contains an element of a certain type
+////////////////////////////////////////////////////////////////////////////////
+
+bool TRI_ContainsBarrierList (TRI_barrier_list_t* container, TRI_barrier_type_e type) {
+  TRI_barrier_t* ptr;
+
+  TRI_LockSpin(&container->_lock);
+
+  ptr = container->_begin;
+
+  while (ptr != NULL) {
+    if (ptr->_type == type) {
+      return true;
+    }
+    ptr = ptr->_next;
+  }
+
+  TRI_UnlockSpin(&container->_lock);
+
+  return false;
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 /// @brief creates a new barrier element
 ////////////////////////////////////////////////////////////////////////////////
@@ -90,32 +169,11 @@ TRI_barrier_t* TRI_CreateBarrierElementZ (TRI_barrier_list_t* container,
   }
 
   element->base._type = TRI_BARRIER_ELEMENT;
-  element->base._container = container;
 
   element->_line = line;
   element->_filename = filename;
 
-  TRI_LockSpin(&container->_lock);
-
-  // empty list
-  if (container->_end == NULL) {
-    element->base._next = NULL;
-    element->base._prev = NULL;
-
-    container->_begin = &element->base;
-    container->_end = &element->base;
-  }
-
-  // add to the end
-  else {
-    element->base._next = NULL;
-    element->base._prev = container->_end;
-
-    container->_end->_next = &element->base;
-    container->_end = &element->base;
-  }
-
-  TRI_UnlockSpin(&container->_lock);
+  LinkBarrierElement(&element->base, container);
 
   return &element->base;
 }
@@ -131,87 +189,75 @@ TRI_barrier_t* TRI_CreateBarrierDatafile (TRI_barrier_list_t* container,
   TRI_barrier_datafile_cb_t* element;
 
   element = TRI_Allocate(TRI_UNKNOWN_MEM_ZONE, sizeof(TRI_barrier_datafile_cb_t), false);
+
   if (!element) {
     return NULL;
   }
 
   element->base._type = TRI_BARRIER_DATAFILE_CALLBACK;
-  element->base._container = container;
 
   element->_datafile = datafile;
   element->_data = data;
 
   element->callback = callback;
 
-  TRI_LockSpin(&container->_lock);
-
-  // empty list
-  if (container->_end == NULL) {
-    element->base._next = NULL;
-    element->base._prev = NULL;
-
-    container->_begin = &element->base;
-    container->_end = &element->base;
-  }
-
-  // add to the end
-  else {
-    element->base._next = NULL;
-    element->base._prev = container->_end;
-
-    container->_end->_next = &element->base;
-    container->_end = &element->base;
-  }
-
-  TRI_UnlockSpin(&container->_lock);
+  LinkBarrierElement(&element->base, container);
 
   return &element->base;
 }
 
 ////////////////////////////////////////////////////////////////////////////////
-/// @brief creates a new collection deletion barrier
+/// @brief creates a new collection unload barrier
 ////////////////////////////////////////////////////////////////////////////////
 
-TRI_barrier_t* TRI_CreateBarrierCollection (TRI_barrier_list_t* container,
-                                            struct TRI_collection_s* collection,
-                                            bool (*callback) (struct TRI_collection_s*, void*),
-                                            void* data) {
+TRI_barrier_t* TRI_CreateBarrierUnloadCollection (TRI_barrier_list_t* container,
+                                                  struct TRI_collection_s* collection,
+                                                  bool (*callback) (struct TRI_collection_s*, void*),
+                                                  void* data) {
   TRI_barrier_collection_cb_t* element;
 
   element = TRI_Allocate(TRI_UNKNOWN_MEM_ZONE, sizeof(TRI_barrier_collection_cb_t), false);
+
   if (!element) {
     return NULL;
   }
 
-  element->base._type = TRI_BARRIER_COLLECTION_CALLBACK;
-  element->base._container = container;
+  element->base._type = TRI_BARRIER_COLLECTION_UNLOAD_CALLBACK;
 
   element->_collection = collection;
   element->_data = data;
 
   element->callback = callback;
 
-  TRI_LockSpin(&container->_lock);
+  LinkBarrierElement(&element->base, container);
 
-  // empty list
-  if (container->_end == NULL) {
-    element->base._next = NULL;
-    element->base._prev = NULL;
+  return &element->base;
+}
 
-    container->_begin = &element->base;
-    container->_end = &element->base;
+////////////////////////////////////////////////////////////////////////////////
+/// @brief creates a new collection drop barrier
+////////////////////////////////////////////////////////////////////////////////
+
+TRI_barrier_t* TRI_CreateBarrierDropCollection (TRI_barrier_list_t* container,
+                                                struct TRI_collection_s* collection,
+                                                bool (*callback) (struct TRI_collection_s*, void*),
+                                                void* data) {
+  TRI_barrier_collection_cb_t* element;
+
+  element = TRI_Allocate(TRI_UNKNOWN_MEM_ZONE, sizeof(TRI_barrier_collection_cb_t), false);
+
+  if (!element) {
+    return NULL;
   }
 
-  // add to the end
-  else {
-    element->base._next = NULL;
-    element->base._prev = container->_end;
+  element->base._type = TRI_BARRIER_COLLECTION_DROP_CALLBACK;
 
-    container->_end->_next = &element->base;
-    container->_end = &element->base;
-  }
+  element->_collection = collection;
+  element->_data = data;
 
-  TRI_UnlockSpin(&container->_lock);
+  element->callback = callback;
+
+  LinkBarrierElement(&element->base, container);
 
   return &element->base;
 }
diff --git a/arangod/VocBase/barrier.h b/arangod/VocBase/barrier.h
index 993be3d163..d6a6d3fa73 100644
--- a/arangod/VocBase/barrier.h
+++ b/arangod/VocBase/barrier.h
@@ -58,7 +58,8 @@ struct TRI_datafile_s;
 typedef enum {
   TRI_BARRIER_ELEMENT,
   TRI_BARRIER_DATAFILE_CALLBACK,
-  TRI_BARRIER_COLLECTION_CALLBACK,
+  TRI_BARRIER_COLLECTION_UNLOAD_CALLBACK,
+  TRI_BARRIER_COLLECTION_DROP_CALLBACK,
 }
 TRI_barrier_type_e;
 
@@ -153,6 +154,12 @@ void TRI_InitBarrierList (TRI_barrier_list_t* container, struct TRI_doc_collecti
 
 void TRI_DestroyBarrierList (TRI_barrier_list_t* container);
 
+////////////////////////////////////////////////////////////////////////////////
+/// @brief check whether the barrier list contains an element of a certain type
+////////////////////////////////////////////////////////////////////////////////
+
+bool TRI_ContainsBarrierList (TRI_barrier_list_t* container, TRI_barrier_type_e type);
+
 ////////////////////////////////////////////////////////////////////////////////
 /// @brief creates a new barrier element
 ////////////////////////////////////////////////////////////////////////////////
@@ -173,13 +180,22 @@ TRI_barrier_t* TRI_CreateBarrierDatafile (TRI_barrier_list_t* container,
                                           void* data);
 
 ////////////////////////////////////////////////////////////////////////////////
-/// @brief creates a new collection deletion barrier
+/// @brief creates a new collection unload barrier
 ////////////////////////////////////////////////////////////////////////////////
 
-TRI_barrier_t* TRI_CreateBarrierCollection (TRI_barrier_list_t* container,
-                                            struct TRI_collection_s* collection,
-                                            bool (*callback) (struct TRI_collection_s*, void*),
-                                            void* data);
+TRI_barrier_t* TRI_CreateBarrierUnloadCollection (TRI_barrier_list_t* container,
+                                                  struct TRI_collection_s* collection,
+                                                  bool (*callback) (struct TRI_collection_s*, void*),
+                                                  void* data);
+
+////////////////////////////////////////////////////////////////////////////////
+/// @brief creates a new collection drop barrier
+////////////////////////////////////////////////////////////////////////////////
+
+TRI_barrier_t* TRI_CreateBarrierDropCollection (TRI_barrier_list_t* container,
+                                                struct TRI_collection_s* collection,
+                                                bool (*callback) (struct TRI_collection_s*, void*),
+                                                void* data);
 
 ////////////////////////////////////////////////////////////////////////////////
 /// @brief removes and frees a barrier element or datafile deletion marker
diff --git a/arangod/VocBase/compactor.c b/arangod/VocBase/compactor.c
index f2ca6f8347..2809b17d07 100644
--- a/arangod/VocBase/compactor.c
+++ b/arangod/VocBase/compactor.c
@@ -453,19 +453,29 @@ static void CompactifySimCollection (TRI_sim_collection_t* sim) {
 ////////////////////////////////////////////////////////////////////////////////
 
 static void CleanupSimCollection (TRI_sim_collection_t* sim) {
-  TRI_barrier_list_t* container;
-  TRI_barrier_t* element;
-  bool deleted;
+  // loop until done
+  while (true) {
+    TRI_barrier_list_t* container;
+    TRI_barrier_t* element;
+    bool hasUnloaded = false;
 
-  container = &sim->base._barrierList;
-  element = NULL;
+    container = &sim->base._barrierList;
+    element = NULL;
 
-  // check and remove a callback elements at the beginning of the list
-  TRI_LockSpin(&container->_lock);
+    // check and remove a callback elements at the beginning of the list
+    TRI_LockSpin(&container->_lock);
+
+    if (container->_begin == NULL || container->_begin->_type == TRI_BARRIER_ELEMENT) {
+      // did not find anything on top of the barrier list or found an element marker
+      // this means we must exit
+      TRI_UnlockSpin(&container->_lock);
+      return;
+    }
 
-  if (container->_begin != NULL && container->_begin->_type != TRI_BARRIER_ELEMENT) {
     element = container->_begin;
+    assert(element);
 
+    // found an element to go on with
     container->_begin = element->_next;
 
     if (element->_next == NULL) {
@@ -474,43 +484,52 @@ static void CleanupSimCollection (TRI_sim_collection_t* sim) {
     else {
       element->_next->_prev = NULL;
     }
-  }
 
-  TRI_UnlockSpin(&container->_lock);
+    TRI_UnlockSpin(&container->_lock);
 
-  if (element == NULL) {
-    return;
-  }
+    // execute callback, sone of the callbacks might delete or free our collection
+    if (element->_type == TRI_BARRIER_DATAFILE_CALLBACK) {
+      TRI_barrier_datafile_cb_t* de;
 
-  // the callback might delete our collection
-  deleted = false;
+      de = (TRI_barrier_datafile_cb_t*) element;
 
-  // execute callback
-  if (element->_type == TRI_BARRIER_DATAFILE_CALLBACK) {
-    TRI_barrier_datafile_cb_t* de;
+      de->callback(de->_datafile, de->_data);
+      TRI_Free(TRI_UNKNOWN_MEM_ZONE, element);
+      // next iteration
+    }
+    else if (element->_type == TRI_BARRIER_COLLECTION_UNLOAD_CALLBACK) {
+      // collection is unloaded
+      TRI_barrier_collection_cb_t* ce;
 
-    de = (TRI_barrier_datafile_cb_t*) element;
+      ce = (TRI_barrier_collection_cb_t*) element;
+      hasUnloaded = ce->callback(ce->_collection, ce->_data);
+      TRI_Free(TRI_UNKNOWN_MEM_ZONE, element);
+      
+      if (hasUnloaded) {
+        // this has unloaded and freed the collection
+        return;
+      }
+    }
+    else if (element->_type == TRI_BARRIER_COLLECTION_DROP_CALLBACK) {
+      // collection is dropped
+      TRI_barrier_collection_cb_t* ce;
 
-    de->callback(de->_datafile, de->_data);
-    TRI_Free(TRI_UNKNOWN_MEM_ZONE, element);
-  }
-  else if (element->_type == TRI_BARRIER_COLLECTION_CALLBACK) {
-    TRI_barrier_collection_cb_t* ce;
+      ce = (TRI_barrier_collection_cb_t*) element;
+      hasUnloaded = ce->callback(ce->_collection, ce->_data);
+      TRI_Free(TRI_UNKNOWN_MEM_ZONE, element);
 
-    ce = (TRI_barrier_collection_cb_t*) element;
-    deleted = ce->callback(ce->_collection, ce->_data);
-    TRI_Free(TRI_UNKNOWN_MEM_ZONE, element);
-  }
-  else {
-    LOG_FATAL("unknown barrier type '%d'", (int) element->_type);
-    TRI_Free(TRI_UNKNOWN_MEM_ZONE, element);
-  }
+      if (hasUnloaded) {
+        // this has dropped the collection
+        return;
+      }
+    }
+    else {
+      // unknown type
+      LOG_FATAL("unknown barrier type '%d'", (int) element->_type);
+      TRI_Free(TRI_UNKNOWN_MEM_ZONE, element);
+    }
 
-  // try again
-  if (! deleted) {
-    // TODO FIXME: this might lead to infinite recursion
-    // can this be replaced with     while (++iterations < MAX_ITERATIONS) { /* do cleanup */ } ?
-    CleanupSimCollection(sim);
+    // next iteration
   }
 }
 
diff --git a/arangod/VocBase/vocbase.c b/arangod/VocBase/vocbase.c
index 74b3211462..b4b4bfd114 100644
--- a/arangod/VocBase/vocbase.c
+++ b/arangod/VocBase/vocbase.c
@@ -836,10 +836,19 @@ static int LoadCollectionVocBase (TRI_vocbase_t* vocbase, TRI_vocbase_col_t* col
   // someone is trying to unload the collection, cancel this,
   // release the WRITE lock and try again
   if (collection->_status == TRI_VOC_COL_STATUS_UNLOADING) {
+    // check if there is a deferred drop action going on for this collection
+    if (TRI_ContainsBarrierList(&collection->_collection->_barrierList, TRI_BARRIER_COLLECTION_DROP_CALLBACK)) {
+      // drop call going on, we must abort
+      TRI_WRITE_UNLOCK_STATUS_VOCBASE_COL(collection);
+
+      return TRI_set_errno(TRI_ERROR_ARANGO_COLLECTION_NOT_FOUND);
+    }
+
+    // no drop action found, go on
     collection->_status = TRI_VOC_COL_STATUS_LOADED;
+
     TRI_WRITE_UNLOCK_STATUS_VOCBASE_COL(collection);
     
-    // TODO: might this cause endless recursion in some obscure cases??
     return LoadCollectionVocBase(vocbase, collection);
   }
 
@@ -1491,10 +1500,10 @@ int TRI_UnloadCollectionVocBase (TRI_vocbase_t* vocbase, TRI_vocbase_col_t* coll
   collection->_status = TRI_VOC_COL_STATUS_UNLOADING;
 
   // added callback for unload
-  TRI_CreateBarrierCollection(&collection->_collection->_barrierList,
-                              &collection->_collection->base,
-                              UnloadCollectionCallback,
-                              collection);
+  TRI_CreateBarrierUnloadCollection(&collection->_collection->_barrierList,
+                                    &collection->_collection->base,
+                                    UnloadCollectionCallback,
+                                    collection);
 
   // release locks
   TRI_WRITE_UNLOCK_STATUS_VOCBASE_COL(collection);
@@ -1591,10 +1600,10 @@ int TRI_DropCollectionVocBase (TRI_vocbase_t* vocbase, TRI_vocbase_col_t* collec
     TRI_WRITE_UNLOCK_STATUS_VOCBASE_COL(collection);
 
     // added callback for dropping
-    TRI_CreateBarrierCollection(&collection->_collection->_barrierList,
-                                &collection->_collection->base,
-                                DropCollectionCallback,
-                                collection);
+    TRI_CreateBarrierDropCollection(&collection->_collection->_barrierList,
+                                    &collection->_collection->base,
+                                    DropCollectionCallback,
+                                    collection);
 
     return TRI_ERROR_NO_ERROR;
   }