diff --git a/collects/mzlib/class.ss b/collects/mzlib/class.ss
index baf7705..7113357 100644
--- a/collects/mzlib/class.ss
+++ b/collects/mzlib/class.ss
@@ -550,10 +550,11 @@
 									  (syntax #f)
 									  (with-syntax ([defexp (stx-car (stx-cdr idp))])
 									    (syntax (lambda () defexp)))))
-								    (syntax->list (syntax (idp ...))))])
+								    (syntax->list (syntax (idp ...))))]
+							      [class-name class-name])
 						  (syntax/loc e 
 						    (begin 
-						      (set! id (extract-arg 'idpos init-args defval))
+						      (set! id (extract-arg 'class-name 'idpos init-args defval))
 						      ...))))]
 					     [(field idp ...)
 					      (syntax/loc e (begin 
@@ -1403,14 +1404,15 @@
 			   (for-class (class-name c))))))))
       o))
 
-  (define (extract-arg name arguments default)
+  (define (extract-arg class-name name arguments default)
     (if (symbol? name)
 	;; Normal mode
 	(let ([a (assq name arguments)])
 	  (cond
 	   [a (cdr a)]
 	   [default (default)]
-	   [else (obj-error "make-object" "no argument for required init variable: ~a" name)]))
+	   [else (obj-error "make-object" "no argument for required init variable: ~a~a" name
+			    (if class-name (format " in class: ~a" class-name) ""))]))
 	;; By-position mode
 	(cond
 	 [(< name (length arguments))
diff --git a/collects/mzlib/private/sigutil.ss b/collects/mzlib/private/sigutil.ss
index 4dab29c..7d2ab3a 100644
--- a/collects/mzlib/private/sigutil.ss
+++ b/collects/mzlib/private/sigutil.ss
@@ -486,6 +486,7 @@
 			   (eof-object? line))
 		      (values lines body vars)]
 		     [(and (stx-pair? line)
+			   (identifier? (stx-car line))
 			   (module-identifier=? (stx-car line) dv-stx))
 		      (syntax-case line ()
 			[(_ (id ...) expr)
@@ -500,6 +501,7 @@
 				       "improper `define-values' clause form"
 				       line)])]
 		     [(and (stx-pair? line)
+			   (identifier? (stx-car line))
 			   (module-identifier=? (stx-car line) begin-stx))
 		      (let ([line-list (stx->list line)])
 			(unless line-list
diff --git a/collects/mzlib/unitsig.ss b/collects/mzlib/unitsig.ss
index c071b5e..a2eee29 100644
--- a/collects/mzlib/unitsig.ss
+++ b/collects/mzlib/unitsig.ss
@@ -299,8 +299,8 @@
 	     (let ([flattened (flatten-signature #f sig)])
 	       (with-syntax ([flattened (map (lambda (x) (datum->syntax-object (syntax signame) x #f))
 					     flattened)])
-		 (syntax
-		  (provide . flattened)))))]))))
+		 (syntax/loc stx
+		   (provide . flattened)))))]))))
   
   (provide define-signature
 	   let-signature