diff --git a/aegisub/src/ass_attachment.cpp b/aegisub/src/ass_attachment.cpp
index 467aacafb..bb8a969f7 100644
--- a/aegisub/src/ass_attachment.cpp
+++ b/aegisub/src/ass_attachment.cpp
@@ -122,7 +122,7 @@ void AssAttachment::Finish() {
 /// @brief Get encoded data to write on file 
 /// @return 
 ///
-const wxString AssAttachment::GetEntryData() {
+const wxString AssAttachment::GetEntryData() const {
 	// Get data
 	const DataVec &dat = data->GetData();
 	int pos = 0;
diff --git a/aegisub/src/ass_attachment.h b/aegisub/src/ass_attachment.h
index 8442158b7..020e4c01d 100644
--- a/aegisub/src/ass_attachment.h
+++ b/aegisub/src/ass_attachment.h
@@ -91,7 +91,7 @@ public:
 	void Import(wxString filename);
 	wxString GetFileName(bool raw=false);
 
-	const wxString GetEntryData();
+	const wxString GetEntryData() const;
 
 	/// @brief DOCME
 	///