diff --git a/arangod/V8Server/v8-collection.cpp b/arangod/V8Server/v8-collection.cpp
index b969ef1773..b7eff74af4 100644
--- a/arangod/V8Server/v8-collection.cpp
+++ b/arangod/V8Server/v8-collection.cpp
@@ -1238,6 +1238,10 @@ static void JS_PropertiesVocbaseCol(
       collection->cid(),
       isModification ? TRI_TRANSACTION_WRITE : TRI_TRANSACTION_READ);
 
+  if (!isModification) {
+    trx.addHint(TRI_TRANSACTION_HINT_NO_USAGE_LOCK, false);
+  }
+  
   int res = trx.begin();
   
   if (res != TRI_ERROR_NO_ERROR) {
diff --git a/arangod/V8Server/v8-replication.cpp b/arangod/V8Server/v8-replication.cpp
index 0d4c0080d9..70c77b7cef 100644
--- a/arangod/V8Server/v8-replication.cpp
+++ b/arangod/V8Server/v8-replication.cpp
@@ -248,7 +248,6 @@ static void JS_SynchronizeReplication(
     database = vocbase->name();
   }
 
-
   std::unordered_map<std::string, bool> restrictCollections;
   if (object->Has(TRI_V8_ASCII_STRING("restrictCollections")) &&
       object->Get(TRI_V8_ASCII_STRING("restrictCollections"))->IsArray()) {
@@ -371,7 +370,21 @@ static void JS_SynchronizeReplication(
     }
 
     result->Set(TRI_V8_ASCII_STRING("collections"), collections);
+  } catch (arangodb::basics::Exception const& ex) {
+    res = ex.code();
+    if (errorMsg.empty()) {
+      errorMsg = std::string("caught exception: ") + ex.what();
+    }
+  } catch (std::exception const& ex) {
+    res = TRI_ERROR_INTERNAL;
+    if (errorMsg.empty()) {
+      errorMsg = std::string("caught exception: ") + ex.what();
+    }
   } catch (...) {
+    res = TRI_ERROR_INTERNAL;
+    if (errorMsg.empty()) {
+      errorMsg = "caught unknown exception";
+    }
   }
 
   if (res != TRI_ERROR_NO_ERROR) {
diff --git a/arangod/V8Server/v8-vocindex.cpp b/arangod/V8Server/v8-vocindex.cpp
index deefdd500c..c3ee93c32f 100644
--- a/arangod/V8Server/v8-vocindex.cpp
+++ b/arangod/V8Server/v8-vocindex.cpp
@@ -932,6 +932,8 @@ static void JS_GetIndexesVocbaseCol(
   SingleCollectionTransaction trx(
       V8TransactionContext::Create(collection->vocbase(), true),
       collection->cid(), TRI_TRANSACTION_READ);
+    
+  trx.addHint(TRI_TRANSACTION_HINT_NO_USAGE_LOCK, false);
 
   int res = trx.begin();
 
@@ -942,12 +944,11 @@ static void JS_GetIndexesVocbaseCol(
   // READ-LOCK start
   trx.lockRead();
 
-  arangodb::LogicalCollection* col = trx.documentCollection();
-  std::string const collectionName(col->name());
+  std::string const collectionName(collection->name());
 
   // get list of indexes
   TransactionBuilderLeaser builder(&trx);
-  auto indexes = col->getIndexes();
+  auto indexes = collection->getIndexes();
 
   trx.finish(res);
   // READ-LOCK end
diff --git a/arangod/VocBase/ReadCache.cpp b/arangod/VocBase/ReadCache.cpp
index f3f9a157e3..a850d8a3a5 100644
--- a/arangod/VocBase/ReadCache.cpp
+++ b/arangod/VocBase/ReadCache.cpp
@@ -133,14 +133,20 @@ ChunkProtector ReadCache::insertAndLease(TRI_voc_rid_t revisionId, uint8_t const
       TRI_ASSERT(p.version() != 0);
       memcpy(p.vpack(), vpack, size); 
       
-      RevisionCacheChunk* chunk = p.chunk();
-      chunk->unqueueWriter();
       TRI_ASSERT(VPackSlice(p.vpack()).isObject());
-      if (result.hasSeenChunk(chunk)) {
-        result.addExisting(p, revisionId);
-      } else {
-        result.add(p, revisionId);
+      RevisionCacheChunk* chunk = p.chunk();
+      try {
+        if (result.hasSeenChunk(chunk)) {
+          result.addExisting(p, revisionId);
+        } else {
+          result.add(p, revisionId);
+        }
+        chunk->unqueueWriter();
+      } catch (...) {
+        chunk->unqueueWriter();
+        throw;
       }
+
       return p;
     }
     
diff --git a/arangod/VocBase/transaction.cpp b/arangod/VocBase/transaction.cpp
index 3b50fca3bd..dcd1184c7f 100644
--- a/arangod/VocBase/transaction.cpp
+++ b/arangod/VocBase/transaction.cpp
@@ -400,11 +400,21 @@ static int UseCollections(TRI_transaction_t* trx, int nestingLevel) {
       } else {
         // use without usage-lock (lock already set externally)
         trxCollection->_collection = trx->_vocbase->lookupCollection(trxCollection->_cid);
+
+        if (trxCollection->_collection == nullptr) {
+          return TRI_ERROR_ARANGO_COLLECTION_NOT_FOUND;
+        }
       }
 
       if (trxCollection->_collection == nullptr) {
         // something went wrong
-        return TRI_errno();
+        int res = TRI_errno();
+
+        if (res == TRI_ERROR_NO_ERROR) {
+          // must return an error
+          res = TRI_ERROR_INTERNAL;
+        }
+        return res;
       }
 
       if (trxCollection->_accessType == TRI_TRANSACTION_WRITE &&
diff --git a/js/server/modules/@arangodb/cluster.js b/js/server/modules/@arangodb/cluster.js
index c6a13f72af..083d6ecad7 100644
--- a/js/server/modules/@arangodb/cluster.js
+++ b/js/server/modules/@arangodb/cluster.js
@@ -130,6 +130,9 @@ function cancelReadLockOnLeader (endpoint, database, lockJobId) {
 // //////////////////////////////////////////////////////////////////////////////
 
 function cancelBarrier (endpoint, database, barrierId) {
+  if (barrierId <= 0) {
+    return true;
+  }
   var url = endpointToURL(endpoint) + '/_db/' + database +
     '/_api/replication/barrier/' + barrierId;
   var r = request({url, method: 'DELETE' });