diff --git a/s48/module-system/overlapping-imports.scm b/s48/module-system/overlapping-imports.scm
new file mode 100644
index 0000000..a1d64b2
--- /dev/null
+++ b/s48/module-system/overlapping-imports.scm
@@ -0,0 +1,26 @@
+(define (overlapping-imports? forms package)
+  (let ((table (make-symbol-table))
+	(dups '()))
+    (for-each
+     (lambda (structure)
+       (for-each-export
+	(lambda (name want-type binding)
+	  (let ((structs (table-ref table name)))
+	    (cond ((not structs)
+		   (table-set! table name (list (structure-name structure))))
+		  ((member (structure-name structure) structs)
+		   #f);seems to happen in real life...
+		  (else (set! dups (cons name dups))
+			(table-set! table
+				    name
+				    (cons (structure-name structure)
+					  (table-ref table name)))))))
+	structure))
+     (package-opens package))
+    (if (not (null? dups))
+	(apply warn "package has overlapping imports" 
+	       package 
+	       (map (lambda (name) (list name (table-ref table name))) dups)))
+    forms))
+    
+(set-optimizer! 'overlapping-imports? overlapping-imports?)
diff --git a/s48/module-system/packages.scm b/s48/module-system/packages.scm
new file mode 100644
index 0000000..bd0d269
--- /dev/null
+++ b/s48/module-system/packages.scm
@@ -0,0 +1,7 @@
+(define-structure overlapping-imports? (export)
+  (open scheme
+	optimizer
+	signals 
+	general-tables 
+	packages-internal)
+  (files overlapping-imports))
\ No newline at end of file