diff --git a/pkgs/racket-test-core/tests/racket/module.rktl b/pkgs/racket-test-core/tests/racket/module.rktl
index b847c08273..eec4effbd8 100644
--- a/pkgs/racket-test-core/tests/racket/module.rktl
+++ b/pkgs/racket-test-core/tests/racket/module.rktl
@@ -2707,6 +2707,19 @@ case of module-leve bindings; it doesn't cover local bindings.
 
 (namespace-attach-module-declaration (current-namespace) ''please-attach-me-successfully (make-base-namespace))
 
+;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; Make sure that a module with an attached instance
+;; cannot be redeclared in the target namespace
+
+(module module-to-attach-elsewhere racket/base)
+(dynamic-require ''module-to-attach-elsewhere #f)
+(eval '(module module-to-attach-elsewhere racket/base)) ; to to redeclare here
+(let ([ns (make-base-namespace)])
+  (namespace-attach-module (current-namespace) ''module-to-attach-elsewhere ns)
+  (err/rt-test (eval '(module module-to-attach-elsewhere racket/base)))
+  (parameterize ([current-namespace ns])
+    (err/rt-test (eval '(module module-to-attach-elsewhere racket/base)))))
+
 ;; ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Check that `local-expand` doesn't make module available in a way
 ;; that allows the module to import itself
diff --git a/racket/src/expander/namespace/module.rkt b/racket/src/expander/namespace/module.rkt
index 01454f7c9c..b19273e876 100644
--- a/racket/src/expander/namespace/module.rkt
+++ b/racket/src/expander/namespace/module.rkt
@@ -289,6 +289,7 @@
                             [declaration-inspector (module-inspector m)]
                             [inspector (namespace-inspector existing-m-ns)]))
   (define mi (make-module-instance m-ns m))
+  (set-module-instance-attached?! mi #t)
   (cond
    [(module-cross-phase-persistent? m)
     (small-hash-set! (namespace-phase-to-namespace m-ns) 0 m-ns)
diff --git a/racket/src/racket/src/startup.inc b/racket/src/racket/src/startup.inc
index 6ddc2f35e1..85d7467aaa 100644
--- a/racket/src/racket/src/startup.inc
+++ b/racket/src/racket/src/startup.inc
@@ -14275,6 +14275,8 @@ static const char *startup_source =
 "(namespace-module-instances the-struct_0)))"
 "                        (raise-argument-error 'struct-copy \"namespace?\" the-struct_0)))))"
 "(let-values(((mi_0)(make-module-instance m-ns_0 m_0)))"
+"(begin"
+"(set-module-instance-attached?! mi_0 #t)"
 "(if(module-cross-phase-persistent? m_0)"
 "(let-values()"
 "(begin"
@@ -14296,7 +14298,9 @@ static const char *startup_source =
 "(small-hash-set!(module-instance-phase-level-to-state mi_0) 0 'started)))"
 "(let-values()"
 "(let-values((()"
-"(begin(small-hash-set!(namespace-phase-to-namespace m-ns_0) 0-phase_0 m-ns_0)(values))))"
+"(begin"
+"(small-hash-set!(namespace-phase-to-namespace m-ns_0) 0-phase_0 m-ns_0)"
+"(values))))"
 "(let-values((()"
 "(begin"
 "(small-hash-set!"
@@ -14309,14 +14313,15 @@ static const char *startup_source =
 "(small-hash-set!(module-instance-phase-level-to-state mi_0) 0 'started)"
 "(values))))"
 "(let-values(((at-phase_0)"
-"(let-values(((or-part_0)(hash-ref(namespace-module-instances ns_0) 0-phase_0 #f)))"
+"(let-values(((or-part_0)"
+"(hash-ref(namespace-module-instances ns_0) 0-phase_0 #f)))"
 "(if or-part_0"
 " or-part_0"
 "(let-values(((at-phase_0)(make-hasheq)))"
 "(begin"
 "(hash-set!(namespace-module-instances ns_0) 0-phase_0 at-phase_0)"
 " at-phase_0))))))"
-"(hash-set! at-phase_0 name_0 mi_0))))))))))))"
+"(hash-set! at-phase_0 name_0 mi_0)))))))))))))"
 "(define-values"
 "(namespace-create-module-instance!)"
 "(lambda(ns_0 name_0 0-phase_0 m_0 mpi_0)"