diff --git a/src/DirManager.cpp b/src/DirManager.cpp
index c39e4b83c..79f26c59e 100644
--- a/src/DirManager.cpp
+++ b/src/DirManager.cpp
@@ -934,15 +934,19 @@ BlockFile *DirManager::NewODDecodeBlockFile(
    return newBlockFile;
 }
 
-bool DirManager::ContainsBlockFile(BlockFile *b)
+bool DirManager::ContainsBlockFile(BlockFile *b) const
 {
-   return b ? mBlockFileHash[b->GetFileName().GetName()] == b : false;
+   if (!b)
+      return false;
+   BlockHash::const_iterator it = mBlockFileHash.find(b->GetFileName().GetName());
+   return it != mBlockFileHash.end() && it->second == b;
 }
 
-bool DirManager::ContainsBlockFile(wxString filepath)
+bool DirManager::ContainsBlockFile(wxString filepath) const
 {
    // check what the hash returns in case the blockfile is from a different project
-   return mBlockFileHash[filepath] != NULL;
+   BlockHash::const_iterator it = mBlockFileHash.find(filepath);
+   return it != mBlockFileHash.end();
 }
 
 // Adds one to the reference count of the block file,
diff --git a/src/DirManager.h b/src/DirManager.h
index cb8a64384..bcc10cac7 100644
--- a/src/DirManager.h
+++ b/src/DirManager.h
@@ -71,9 +71,9 @@ class DirManager: public XMLTagHandler {
                                  sampleCount aliasLen, int aliasChannel, int decodeType);
 
    /// Returns true if the blockfile pointed to by b is contained by the DirManager
-   bool ContainsBlockFile(BlockFile *b);
+   bool ContainsBlockFile(BlockFile *b) const;
    /// Check for existing using filename using complete filename
-   bool ContainsBlockFile(wxString filepath);
+   bool ContainsBlockFile(wxString filepath) const;
 
    // Adds one to the reference count of the block file,
    // UNLESS it is "locked", then it makes a new copy of