diff --git a/src/lib/iter-source.hpp b/src/lib/iter-source.hpp
index f887b4c21..a18de84e0 100644
--- a/src/lib/iter-source.hpp
+++ b/src/lib/iter-source.hpp
@@ -51,6 +51,7 @@
 #include "lib/iter-adapter.hpp"
 #include "lib/itertools.hpp"
 
+#include <boost/type_traits/remove_const.hpp>
 #include <boost/noncopyable.hpp>
 #include <tr1/memory>
 
@@ -259,8 +260,8 @@ namespace lib {
         {
           typedef typename MAP::key_type Key;
           typedef typename MAP::value_type::second_type Val;
-          typedef typename IterSource<const Key>::iterator KeyIter;
-          typedef typename IterSource<      Val>::iterator ValIter;
+          typedef typename IterSource<Key>::iterator KeyIter;
+          typedef typename IterSource<Val>::iterator ValIter;
         };
       
       
@@ -275,8 +276,12 @@ namespace lib {
       struct _PairIterT
         {
           typedef typename IT::value_type PairType;
-          typedef typename PairType::first_type KeyType;
           typedef typename PairType::second_type ValType;
+          typedef typename PairType::first_type ConstKeyType;
+          
+          // since we're returning the keys always by value,
+          // we can strip the const added by the STL map types
+          typedef typename boost::remove_const<ConstKeyType>::type KeyType;
           
           typedef TransformIter<IT,KeyType> KeyIter;
           typedef TransformIter<IT,ValType> ValIter;
@@ -347,12 +352,17 @@ namespace lib {
     
     /** @return a Lumiera Forward Iterator to yield
      *          all \em distinct keys of a Multimap
+     *  @warning we do a full table scan to find
+     *          the distinct keys
      */
     template<class MAP>
     typename _MapT<MAP>::KeyIter
-    eachDistinctKey (MAP&) // map)
+    eachDistinctKey (MAP& map)
     {
-      UNIMPLEMENTED ("standard iter wrapper yielding all distinct keys of a multimap");
+      typedef RangeIter<typename MAP::iterator> Range;
+      
+      Range contents (map.begin(), map.end());
+      return wrapIter (filterRepetitions (takePairFirst(contents)));
     }
     
     
diff --git a/src/proc/mobject/session/placement-index.cpp b/src/proc/mobject/session/placement-index.cpp
index 395e5059e..fb8a12b06 100644
--- a/src/proc/mobject/session/placement-index.cpp
+++ b/src/proc/mobject/session/placement-index.cpp
@@ -305,7 +305,7 @@ namespace session {
       
       /* == access for self-test == */
       
-      typedef lib::IterSource<const PID>::iterator IDIter;
+      typedef lib::IterSource<PID>::iterator IDIter;
       
       PlacementMO* _root_4check ()        { return root_.get(); }
       PlacementMO* _element_4check (ID id){ return base_entry(id).element.get();}
diff --git a/tests/40components.tests b/tests/40components.tests
index cd8b9d9c6..847b9fa5c 100644
--- a/tests/40components.tests
+++ b/tests/40components.tests
@@ -363,6 +363,7 @@ out: (::X...........){13}$
 out: (::00:0.:....00){13}$
 out: (::X...........){13}$
 out: (::00:0.:....00){13}$
+out: distinct_keys::0::1::2::3::4::5::6::7::8::9::10::11::12
 END
 
 
diff --git a/tests/lib/iter-source-test.cpp b/tests/lib/iter-source-test.cpp
index 253b95d6f..3565f9c98 100644
--- a/tests/lib/iter-source-test.cpp
+++ b/tests/lib/iter-source-test.cpp
@@ -33,6 +33,7 @@
 #include <boost/noncopyable.hpp>
 #include <tr1/unordered_map>
 #include <iostream>
+#include <cstdlib>
 #include <string>
 #include <list>
 #include <map>
@@ -50,8 +51,10 @@ namespace test{
   using lib::test::randTime;
   using util::isnil;
   using util::cStr;
+  using std::make_pair;
   using std::string;
   using std::list;
+  using std::rand;
   using std::cout;
   using std::endl;
   
@@ -149,12 +152,16 @@ namespace test{
       
       typedef IterSource<int>::iterator IntIter;
       typedef IterSource<CStr>::iterator StrIter;
-      typedef IterSource<const string>::iterator StringIter;
+      typedef IterSource<string>::iterator StringIter;
       typedef IterSource<Time>::iterator TimeIter;
       
       typedef std::map<string,Time>                TreeMap;
       typedef std::tr1::unordered_map<string,Time> HashMap;
       
+      typedef std::multimap<int,int>               TreeMultimap;
+      typedef std::tr1::unordered_multimap<int,int>HashMultimap;
+      
+      
       virtual void
       run (Arg arg)
         {
@@ -164,6 +171,9 @@ namespace test{
           
           verify_MapWrappers<TreeMap>();
           verify_MapWrappers<HashMap>();
+          
+          verify_MultimapKeyIter<TreeMultimap>();
+          verify_MultimapKeyIter<HashMultimap>();
         }
       
       
@@ -217,8 +227,30 @@ namespace test{
           ASSERT (!sIter && !tIter);
         }
       
+      
+      template<class MAP>
+      void
+      verify_MultimapKeyIter()  ///< @see IterTools_test#verify_filterRepetitions
+        {
+          MAP testMap;
+          for (uint i=0; i<NUM_ELMS; ++i)
+            {
+              uint n = 1 + rand() % 100;
+              do testMap.insert (make_pair (i,n));
+              while (--n);
+            }
+          ASSERT (NUM_ELMS < testMap.size(), "no repetition in test data??");
+          
+          IntIter keys = eachDistinctKey (testMap);
+          
+          cout << "distinct_keys";
+          ASSERT (keys);
+          pullOut (keys);
+          ASSERT (!keys);
+        }
     };
   
+  
   LAUNCHER (IterSource_test, "unit common");