diff --git a/collects/mzlib/private/sigutil.ss b/collects/mzlib/private/sigutil.ss
index 46a62fc..b3d7cd6 100644
--- a/collects/mzlib/private/sigutil.ss
+++ b/collects/mzlib/private/sigutil.ss
@@ -70,7 +70,7 @@
 	   [(symbol? elem) elem]
 	   [(and (pair? elem) (symbol? (car elem)))
 	    (intern-signature (car elem) (cdr elem))]
-	   [else (error)]))
+	   [else (error "intern failed")]))
 	(vector->list (car desc)))
        (map
 	(lambda (elem)
diff --git a/collects/mzlib/process.ss b/collects/mzlib/process.ss
index 4488b11..c0e4c04 100644
--- a/collects/mzlib/process.ss
+++ b/collects/mzlib/process.ss
@@ -28,6 +28,7 @@
 			 'exact
 			 (format "~a /c ~a" cmd argstr))))
       (else (raise-mismatch-error 
+	     who
 	     (format "~a: don't know what shell to use for platform: " who)
 	     (system-type)))))
 
diff --git a/collects/mzlib/thread.ss b/collects/mzlib/thread.ss
index 0bfdce1..8749569 100644
--- a/collects/mzlib/thread.ss
+++ b/collects/mzlib/thread.ss
@@ -60,7 +60,6 @@
 		      (make-exn:application:arity
 		       (format "<procedure-from-consumer-thread>: consumer procedure arity is ~e; provided ~s argument~a"
 			       (procedure-arity f) num (if (= 1 num) "" "s"))
-		       #f #f
 		       (current-continuation-marks)
 		       num
 		       (procedure-arity f)))))