--- orig/ice-9/boot-9.scm
+++ mod/ice-9/boot-9.scm
@@ -1511,10 +1511,22 @@
 	       (module-modified m)
 	       b)))
 
-      ;; Create a new local variable.
-      (let ((local-var (make-undefined-variable)))
-        (module-add! m v local-var)
-        local-var)))
+      ;; No local variable yet, so we need to create a new one.  That
+      ;; new variable is initialized with the old imported value of V,
+      ;; if there is one.  This is required by Section 5.2.1 of R5RS which
+      ;; says that `define' is equivalent to `set!' when V is already bound
+      ;; (of course here we respect module boundaries so this is not exactly
+      ;; a `set!').
+      (let ((imported-var (module-variable m v))
+	    (local-var (or (and (module-binder m)
+				((module-binder m) m v #t))
+			   (begin
+			     (let ((answer (make-undefined-variable)))
+			       (module-add! m v answer)
+			       answer)))))
+	(if (and imported-var (not (variable-bound? local-var)))
+	    (variable-set! local-var (variable-ref imported-var)))
+	local-var)))
 
 ;; module-ensure-local-variable! module symbol
 ;;

--- orig/test-suite/tests/modules.test
+++ mod/test-suite/tests/modules.test
@@ -118,7 +118,16 @@
               (map module-variable
                    (map resolve-interface mods)
                    syms)
-              locals))))
+              locals)))
+
+  (pass-if "redefinition"
+    (let ((m (make-module)))
+      (beautify-user-module! m)
+
+      ;; The previous value of `round' must still be visible at the time the
+      ;; new `round' is defined.
+      (eval '(define round round) m)
+      (eq? (module-ref m 'stat) stat))))