diff --git a/chunkedstorage.cc b/chunkedstorage.cc
index 69b155fe..26e32cde 100644
--- a/chunkedstorage.cc
+++ b/chunkedstorage.cc
@@ -139,6 +139,8 @@ char * Reader::getBlock( uint32_t address, vector< char > & chunk )
     // file.seek( offsets[ chunkIdx ] );
     Mutex::Lock _( file.lock );
     auto bytes = file.map( offsets[ chunkIdx ], 8 );
+    if( bytes == nullptr )
+      throw mapFailed();
     auto qBytes = QByteArray::fromRawData( reinterpret_cast< char * >(bytes), 8 );
     QDataStream in( qBytes );
     in.setByteOrder( QDataStream::LittleEndian );
@@ -153,7 +155,8 @@ char * Reader::getBlock( uint32_t address, vector< char > & chunk )
 
     // vector< unsigned char > compressedData( compressedSize );
     auto chunkDataBytes = file.map( offsets[ chunkIdx ] + 8, compressedSize );
-
+    if( chunkDataBytes == nullptr )
+      throw mapFailed();
     // file.read( &compressedData.front(), compressedData.size() );
     auto autoUnmap = qScopeGuard(
       [ & ] {
diff --git a/chunkedstorage.hh b/chunkedstorage.hh
index b92c6aed..4132e30b 100644
--- a/chunkedstorage.hh
+++ b/chunkedstorage.hh
@@ -25,6 +25,7 @@ DEF_EX( Ex, "Chunked storage exception", std::exception )
 DEF_EX( exFailedToCompressChunk, "Failed to compress a chunk", Ex )
 DEF_EX( exAddressOutOfRange, "The given chunked address is out of range", Ex )
 DEF_EX( exFailedToDecompressChunk, "Failed to decompress a chunk", Ex )
+DEF_EX( mapFailed, "Failed to map/unmap the file", Ex )
 
 /// This class writes data blocks in chunks.
 class Writer