diff --git a/src/eval.c b/src/eval.c
index 3e899db4436..a73700419dd 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -1992,6 +1992,9 @@ signal_error (const char *s, Lisp_Object arg)
   xsignal (Qerror, Fcons (build_string (s), arg));
 }
 
+/* Simplified version of 'define-error' that works with pure
+   objects.  */
+
 void
 define_error (Lisp_Object name, const char *message, Lisp_Object parent)
 {
diff --git a/src/lisp.h b/src/lisp.h
index 9da654cf9af..4217dd9e347 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4867,6 +4867,7 @@ extern AVOID xsignal2 (Lisp_Object, Lisp_Object, Lisp_Object);
 extern AVOID xsignal3 (Lisp_Object, Lisp_Object, Lisp_Object, Lisp_Object);
 extern AVOID signal_error (const char *, Lisp_Object);
 extern AVOID overflow_error (void);
+extern void define_error (Lisp_Object name, const char *message, Lisp_Object parent);
 extern bool FUNCTIONP (Lisp_Object);
 extern Lisp_Object funcall_subr (struct Lisp_Subr *subr, ptrdiff_t numargs, Lisp_Object *arg_vector);
 extern Lisp_Object eval_sub (Lisp_Object form);
@@ -5975,11 +5976,6 @@ maybe_gc (void)
     maybe_garbage_collect ();
 }
 
-/* Simplified version of 'define-error' that works with pure
-   objects.  */
-void
-define_error (Lisp_Object name, const char *message, Lisp_Object parent);
-
 INLINE_HEADER_END
 
 #endif /* EMACS_LISP_H */