diff --git a/cpp/Completer.cpp b/cpp/Completer.cpp
index 2ee50ff9..531234cd 100644
--- a/cpp/Completer.cpp
+++ b/cpp/Completer.cpp
@@ -110,7 +110,7 @@ void Completer::AddCandidatesToDatabase(
     const std::string &filetype,
     const std::string &filepath )
 {
-  std::vector< Candidate *> &candidates =
+  std::vector< const Candidate *> &candidates =
     GetCandidateVector( filetype, filepath );
 
   int num_candidates = new_candidates.size();
@@ -120,8 +120,8 @@ void Completer::AddCandidatesToDatabase(
   for (int i = 0; i < num_candidates; ++i)
   {
     const std::string &candidate_text = new_candidates[ i ];
-    Candidate *&candidate = GetValueElseInsert( candidate_repository_,
-                                                candidate_text, NULL );
+    const Candidate *&candidate = GetValueElseInsert( candidate_repository_,
+                                                      candidate_text, NULL );
     if ( !candidate )
       candidate = new Candidate( candidate_text );
 
@@ -199,7 +199,7 @@ void Completer::ResultsForQueryAndType( const std::string &query,
   foreach ( const FilepathToCandidates::value_type &path_and_candidates,
             *it->second )
   {
-    foreach ( Candidate* candidate, *path_and_candidates.second )
+    foreach ( const Candidate* candidate, *path_and_candidates.second )
     {
       if ( !candidate->MatchesQueryBitset( query_bitset ) )
         continue;
@@ -214,7 +214,7 @@ void Completer::ResultsForQueryAndType( const std::string &query,
 }
 
 
-std::vector< Candidate* >& Completer::GetCandidateVector(
+std::vector< const Candidate* >& Completer::GetCandidateVector(
     const std::string &filetype,
     const std::string &filepath )
 {
@@ -224,11 +224,11 @@ std::vector< Candidate* >& Completer::GetCandidateVector(
   if ( !path_to_candidates )
     path_to_candidates.reset( new FilepathToCandidates() );
 
-  boost::shared_ptr< std::vector< Candidate* > > &candidates =
+  boost::shared_ptr< std::vector< const Candidate* > > &candidates =
     (*path_to_candidates)[ filepath ];
 
   if ( !candidates )
-    candidates.reset( new std::vector< Candidate* >() );
+    candidates.reset( new std::vector< const Candidate* >() );
 
   return *candidates;
 }
diff --git a/cpp/Completer.h b/cpp/Completer.h
index 532673b2..bd01eb21 100644
--- a/cpp/Completer.h
+++ b/cpp/Completer.h
@@ -37,11 +37,13 @@ namespace YouCompleteMe
 typedef boost::python::list Pylist;
 
 // candidate text string -> candidate objects
-typedef boost::unordered_map< std::string, Candidate* > CandidateRepository;
+typedef boost::unordered_map< std::string, const Candidate* >
+          CandidateRepository;
 
 // filepath -> *( *candidate )
 typedef boost::unordered_map< std::string,
-          boost::shared_ptr< std::vector< Candidate* > > > FilepathToCandidates;
+          boost::shared_ptr< std::vector< const Candidate* > > >
+            FilepathToCandidates;
 
 // filetype -> *( filepath -> *( *candidate ) )
 typedef boost::unordered_map< std::string,
@@ -93,7 +95,7 @@ private:
                                const std::string &filetype,
                                std::vector< Result > &results ) const;
 
-  std::vector< Candidate* >& GetCandidateVector(
+  std::vector< const Candidate* >& GetCandidateVector(
       const std::string &filetype,
       const std::string &filepath );