diff --git a/include/wx/fs_mem.h b/include/wx/fs_mem.h
index 3a89e19e1b..9070967326 100644
--- a/include/wx/fs_mem.h
+++ b/include/wx/fs_mem.h
@@ -90,7 +90,9 @@ public:
     }
 
 #if wxUSE_IMAGE
-    static void AddFile(const wxString& filename, wxImage& image, long type);
+    static void AddFile(const wxString& filename,
+                        const wxImage& image,
+                        long type);
 
     static void AddFile(const wxString& filename,
                         const wxBitmap& bitmap,
diff --git a/src/common/fs_mem.cpp b/src/common/fs_mem.cpp
index 8e77fde518..de45ca8b96 100644
--- a/src/common/fs_mem.cpp
+++ b/src/common/fs_mem.cpp
@@ -216,7 +216,9 @@ bool wxMemoryFSHandlerBase::CheckHash(const wxString& filename)
 
 #if wxUSE_IMAGE
 /*static*/ void
-wxMemoryFSHandler::AddFile(const wxString& filename, wxImage& image, long type)
+wxMemoryFSHandler::AddFile(const wxString& filename,
+                           const wxImage& image,
+                           long type)
 {
     if (!CheckHash(filename)) return;
 
@@ -232,7 +234,10 @@ wxMemoryFSHandler::AddFile(const wxString& filename, wxImage& image, long type)
     }
 }
 
-/*static*/ void wxMemoryFSHandler::AddFile(const wxString& filename, const wxBitmap& bitmap, long type)
+/*static*/ void
+wxMemoryFSHandler::AddFile(const wxString& filename,
+                           const wxBitmap& bitmap,
+                           long type)
 {
     wxImage img = bitmap.ConvertToImage();
     AddFile(filename, img, type);