diff --git a/collects/deinprogramm/signature/module-begin.rkt b/collects/deinprogramm/signature/module-begin.rkt
index cafb51ea1c..e56249b3b3 100644
--- a/collects/deinprogramm/signature/module-begin.rkt
+++ b/collects/deinprogramm/signature/module-begin.rkt
@@ -48,11 +48,16 @@
 				 (raise-syntax-error #f
 						     "Nach dem : sollte ein Bezeichner stehen; da steht was anderes."
 						     #'?id))
-			       (when (bound-identifier-mapping-get table #'?id (lambda () #f))
-				 (raise-syntax-error #f
-						     "Zweite Signaturdeklaration für denselben Namen."
-						     maybe))
-			       (bound-identifier-mapping-put! table #'?id #'?cnt)
+			       (cond
+				((bound-identifier-mapping-get table #'?id (lambda () #f))
+				 => (lambda (old-cnt-stx)
+				      (unless (equal? (syntax->datum old-cnt-stx)
+							(syntax->datum #'?cnt))
+					(raise-syntax-error #f
+							    "Zweite Signaturdeklaration für denselben Namen."
+							    maybe))))
+				(else
+				 (bound-identifier-mapping-put! table #'?id #'?cnt)))
 			       #f))
 			    ((: ?id)
 			     (raise-syntax-error #f "Bei dieser Signaturdeklaration fehlt die Signatur" maybe))
diff --git a/collects/lang/private/teach-module-begin.rkt b/collects/lang/private/teach-module-begin.rkt
index 75912c23f7..86fb3dbf81 100644
--- a/collects/lang/private/teach-module-begin.rkt
+++ b/collects/lang/private/teach-module-begin.rkt
@@ -55,11 +55,16 @@
 						     #'?id))
 			       
 			       (let ((real-id (first-order->higher-order #'?id)))
-				 (when (bound-identifier-mapping-get table real-id (lambda () #f))
-				   (raise-syntax-error #f
-						       "Second signature declaration for the same name."
-						       maybe))
-				 (bound-identifier-mapping-put! table real-id #'?cnt)
+				 (cond
+				  ((bound-identifier-mapping-get table real-id (lambda () #f))
+				   => (lambda (old-cnt-stx)
+					(unless (equal? (syntax->datum old-cnt-stx)
+							(syntax->datum #'?cnt))
+					  (raise-syntax-error #f
+							      "Second signature declaration for the same name."
+							      maybe))))
+				  (else
+				   (bound-identifier-mapping-put! table real-id #'?cnt)))
 				 #f)))
 			    ((: ?id)
 			     (raise-syntax-error #f "Signature declaration is missing a signature." maybe))