diff --git a/libs/image/tiles3/swap/kis_memory_window.cpp b/libs/image/tiles3/swap/kis_memory_window.cpp
--- a/libs/image/tiles3/swap/kis_memory_window.cpp
+++ b/libs/image/tiles3/swap/kis_memory_window.cpp
@@ -120,5 +120,7 @@
 
         adjustingWindow->window = m_file.map(adjustingWindow->chunk.m_begin,
                                              adjustingWindow->chunk.size());
+
+        KIS_ASSERT(adjustingWindow->window != nullptr);
     }
 }