diff --git a/src/xfns.c b/src/xfns.c
index 7427144b103..7ec6025ab66 100644
--- a/src/xfns.c
+++ b/src/xfns.c
@@ -1398,10 +1398,9 @@ x_set_mouse_color (struct frame *f, Lisp_Object arg, Lisp_Object oldval)
   if (x_had_errors_p (dpy))
     {
       const char *bad_cursor_name = NULL;
-      /* Bounded by X_ERROR_MESSAGE_SIZE in xterm.c.  */
-      size_t message_length = strlen (cursor_data.error_string);
-      char *xmessage = alloca (1 + message_length);
-      memcpy (xmessage, cursor_data.error_string, message_length);
+      char xmessage[X_ERROR_MESSAGE_SIZE];
+      eassert (strlen (cursor_data.error_string) < sizeof xmessage);
+      strcpy (xmessage, cursor_data.error_string);
 
       x_uncatch_errors_after_check ();
 
diff --git a/src/xterm.c b/src/xterm.c
index 1401693541c..b2a0d2cadcc 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -26321,8 +26321,6 @@ x_unwind_errors_to (int depth)
     x_uncatch_errors ();
 }
 
-#define X_ERROR_MESSAGE_SIZE 200
-
 /* An X error handler which stores the error message in the first
    applicable handler in the x_error_message stack.  This is called
    from *x_error_handler if an x_catch_errors for DISPLAY is in
diff --git a/src/xterm.h b/src/xterm.h
index 962c856e772..28b720c9222 100644
--- a/src/xterm.h
+++ b/src/xterm.h
@@ -129,6 +129,8 @@ typedef GtkWidget *xt_or_gtk_widget;
 #include "dispextern.h"
 #include "termhooks.h"
 
+enum { X_ERROR_MESSAGE_SIZE = 200 };
+
 INLINE_HEADER_BEGIN
 
 /* Black and white pixel values for the screen which frame F is on.  */