diff --git a/arangod/Indexes/SkiplistIndex.cpp b/arangod/Indexes/SkiplistIndex.cpp
index 2d58f8b92f..734743203f 100644
--- a/arangod/Indexes/SkiplistIndex.cpp
+++ b/arangod/Indexes/SkiplistIndex.cpp
@@ -200,7 +200,7 @@ static int FillLookupOperator (TRI_index_operator_t* slOperator,
 // --SECTION--                                                    public methods
 // -----------------------------------------------------------------------------
 
-size_t SkiplistIterator::size () {
+size_t SkiplistIterator::size () const {
   return _intervals.size();
 }
 
@@ -223,7 +223,7 @@ void SkiplistIterator::initCursor () {
   }
 }
 
-bool SkiplistIterator::hasNext () {
+bool SkiplistIterator::hasNext () const {
   if (_reverse) {
     return hasPrevIteration();
   }
@@ -499,7 +499,7 @@ void SkiplistIterator::findHelper (
 /// interval or before it - without advancing the iterator.
 ////////////////////////////////////////////////////////////////////////////////
 
-bool SkiplistIterator::hasPrevIteration () {
+bool SkiplistIterator::hasPrevIteration () const {
   // ...........................................................................
   // if we have more intervals than the one we are currently working
   // on then of course we have a previous doc, because intervals are nonempty.
@@ -523,7 +523,7 @@ bool SkiplistIterator::hasPrevIteration () {
 /// interval - without advancing the iterator.
 ////////////////////////////////////////////////////////////////////////////////
 
-bool SkiplistIterator::hasNextIteration () {
+bool SkiplistIterator::hasNextIteration () const {
   if (_cursor == nullptr) {
     return false;
   }
@@ -814,7 +814,7 @@ size_t SkiplistIndex::elementSize () const {
 ////////////////////////////////////////////////////////////////////////////////
 
 int SkiplistIndex::KeyElementComparator::operator() (TRI_skiplist_index_key_t const* leftKey,
-                                      TRI_index_element_t const* rightElement) {
+                                                     TRI_index_element_t const* rightElement) const {
 
   TRI_ASSERT(nullptr != leftKey);
   TRI_ASSERT(nullptr != rightElement);
@@ -841,8 +841,8 @@ int SkiplistIndex::KeyElementComparator::operator() (TRI_skiplist_index_key_t co
 ////////////////////////////////////////////////////////////////////////////////
 
 int SkiplistIndex::ElementElementComparator::operator() (TRI_index_element_t const* leftElement,
-                                          TRI_index_element_t const* rightElement,
-                                          triagens::basics::SkipListCmpType cmptype) {
+                                                         TRI_index_element_t const* rightElement,
+                                                         triagens::basics::SkipListCmpType cmptype) const {
 
   TRI_ASSERT(nullptr != leftElement);
   TRI_ASSERT(nullptr != rightElement);
diff --git a/arangod/Indexes/SkiplistIndex.h b/arangod/Indexes/SkiplistIndex.h
index 9222162ed6..f06f23f006 100644
--- a/arangod/Indexes/SkiplistIndex.h
+++ b/arangod/Indexes/SkiplistIndex.h
@@ -81,7 +81,8 @@ namespace triagens {
 
           SkiplistIteratorInterval ()
             : _leftEndPoint(nullptr),
-              _rightEndPoint(nullptr) { }
+              _rightEndPoint(nullptr) { 
+          }
         };
 
 // -----------------------------------------------------------------------------
@@ -90,7 +91,7 @@ namespace triagens {
       
       private:
 
-        SkiplistIndex* const _index;
+        SkiplistIndex const* _index;
         size_t _currentInterval; // starts with 0, current interval used
         bool _reverse;
         Node* _cursor;
@@ -102,16 +103,16 @@ namespace triagens {
       
       public:
 
-        SkiplistIterator (
-          SkiplistIndex* const idx,
-          bool reverse
-        ) : _index(idx) ,
+        SkiplistIterator (SkiplistIndex const* idx,
+                          bool reverse) 
+          : _index(idx) ,
             _currentInterval(0),
             _reverse(reverse),
             _cursor(nullptr) {
         }
 
-        ~SkiplistIterator () {}
+        ~SkiplistIterator () {
+        }
 
         // always holds the last node returned, initially equal to
         // the _leftEndPoint of the first interval (or the 
@@ -131,9 +132,9 @@ namespace triagens {
       
       public:
         
-        size_t size ();
+        size_t size () const;
 
-        bool hasNext ();
+        bool hasNext () const;
 
         TRI_index_element_t* next ();
 
@@ -150,10 +151,10 @@ namespace triagens {
 
       private:
 
-        bool hasPrevIteration ();
+        bool hasPrevIteration () const;
         TRI_index_element_t* prevIteration ();
 
-        bool hasNextIteration ();
+        bool hasNextIteration () const;
         TRI_index_element_t* nextIteration ();
 
         bool findHelperIntervalIntersectionValid (
@@ -162,9 +163,7 @@ namespace triagens {
           SkiplistIteratorInterval& interval
         );
 
-        bool findHelperIntervalValid (
-          SkiplistIteratorInterval const& interval
-        );
+        bool findHelperIntervalValid (SkiplistIteratorInterval const& interval);
     };
 
 // -----------------------------------------------------------------------------
@@ -175,7 +174,7 @@ namespace triagens {
 
       struct KeyElementComparator {
         int operator() (TRI_skiplist_index_key_t const* leftKey,
-                        TRI_index_element_t const* rightElement);
+                        TRI_index_element_t const* rightElement) const;
 
         KeyElementComparator (SkiplistIndex* idx) {
           _idx = idx;
@@ -189,7 +188,7 @@ namespace triagens {
       struct ElementElementComparator {
         int operator() (TRI_index_element_t const* leftElement,
                         TRI_index_element_t const* rightElement,
-                       triagens::basics::SkipListCmpType cmptype);
+                        triagens::basics::SkipListCmpType cmptype) const;
 
         ElementElementComparator (SkiplistIndex* idx) {
           _idx = idx;
diff --git a/lib/Basics/SkipList.h b/lib/Basics/SkipList.h
index 67930d347a..9dec63ec8d 100644
--- a/lib/Basics/SkipList.h
+++ b/lib/Basics/SkipList.h
@@ -245,7 +245,7 @@ namespace triagens {
 /// @brief return the successor node or nullptr if last node
 ////////////////////////////////////////////////////////////////////////////////
 
-        Node* nextNode (Node* node) {
+        Node* nextNode (Node* node) const {
           return node->_next[0];
         }