diff --git a/src/error.h b/src/error.h
--- a/src/error.h
+++ b/src/error.h
@@ -44,6 +44,9 @@ public:
 	~ErrorMessageData();
 	ErrorMessageData(StringID summary_msg, StringID detailed_msg, uint duration = 0, int x = 0, int y = 0, const GRFFile *textref_stack_grffile = nullptr, uint textref_stack_size = 0, const uint32 *textref_stack = nullptr);
 
+	/* Remove the copy assignment, as the default implementation will not do the right thing. */
+	ErrorMessageData &operator=(ErrorMessageData &rhs) = delete;
+
 	/** Check whether error window shall display a company manager face */
 	bool HasFace() const { return face != INVALID_COMPANY; }