diff --git a/lib/chibi/iset/constructors.scm b/lib/chibi/iset/constructors.scm
index ec72f3e6..6c09d553 100644
--- a/lib/chibi/iset/constructors.scm
+++ b/lib/chibi/iset/constructors.scm
@@ -171,10 +171,19 @@
              (iset-node-extract node (+ end 1) (iset-end node)))))
 
 (define (iset-node-extract node start end)
-  (let ((bits (and (iset-bits node)
-                   (arithmetic-shift (iset-bits node)
-                                     (- (iset-start node) start)))))
-    (%make-iset start end bits #f #f)))
+  (cond
+   ((iset-bits node)
+    => (lambda (node-bits)
+         (let* ((bits
+                 (bitwise-and
+                  (arithmetic-shift node-bits (- (iset-start node) start))
+                  (range->bits start end)))
+                (new-end (min end (+ start (integer-length bits)))))
+           (%make-iset start new-end bits #f #f))))
+   (else
+    (%make-iset (max start (iset-start node))
+                (min end (iset-end node))
+                #f #f #f))))
 
 (define (iset-adjoin! iset . ls)
   (list->iset! ls iset))
diff --git a/tests/iset-tests.scm b/tests/iset-tests.scm
index e7b4b160..3fd18fac 100644
--- a/tests/iset-tests.scm
+++ b/tests/iset-tests.scm
@@ -102,5 +102,46 @@
 
 (test-assert (iset= (iset-union (iset 1 3) (iset 3 4)) (iset 1 3 4)))
 (test-assert (iset= (iset-union (iset 3) (iset 1 3)) (iset 1 3)))
+(test-assert (iset= (iset-union (iset 1 4) (iset 3 4 5)) (iset 1 3 4 5)))
+
+(test '(1 2 3 4 5 6 7 8) (iset->list (iset 1 2 3 4 5 6 7 8)))
+(test '(1 3 4 5 6 7 8) (iset->list (iset 1 3 4 5 6 7 8)))
+(test '(1 2 4 5 6 7 8) (iset->list (iset 1 2 4 5 6 7 8)))
+(test '(1 2 3 5 6 7 8) (iset->list (iset 1 2 3 5 6 7 8)))
+(test '(1 2 3 4 6 7 8) (iset->list (iset 1 2 3 4 6 7 8)))
+(test '(1 2 3 4 5 7 8) (iset->list (iset 1 2 3 4 5 7 8)))
+(test '(1 2 3 4 5 6 8) (iset->list (iset 1 2 3 4 5 6 8)))
+
+(test '(1 2 3 4 5 6 7 8)
+    (iset->list (iset-union (iset 1 2 3 4) (iset 5 6 7 8))))
+(test '(1 3 4 5 6 7 8)
+    (iset->list (iset-union (iset 1 3 4) (iset 5 6 7 8))))
+(test '(1 2 4 5 6 7 8)
+    (iset->list (iset-union (iset 1 2 4) (iset 5 6 7 8))))
+(test '(1 2 3 5 6 7 8)
+    (iset->list (iset-union (iset 1 2 3) (iset 5 6 7 8))))
+(test '(1 2 3 4 6 7 8)
+    (iset->list (iset-union (iset 1 2 3 4) (iset 6 7 8))))
+(test '(1 2 3 4 5 7 8)
+    (iset->list (iset-union (iset 1 2 3 4) (iset 5 7 8))))
+(test '(1 2 3 4 5 6 8)
+    (iset->list (iset-union (iset 1 2 3 4) (iset 5 6 8))))
+(test '(1 2 3 6 7 8)
+    (iset->list (iset-union (iset 1 2 3) (iset 6 7 8))))
+(test '(1 3 6 8)
+    (iset->list (iset-union (iset 1 3) (iset 6 8))))
+
+(test '(1 2 3 4 1001 1002 1003 1004 2001 2002 2003 2004)
+    (iset->list (iset-union (iset 1 2 3 4 1001 1002)
+                            (iset 1003 1004 2001 2002 2003 2004))))
+(test '(1 2 4 1001 1002 1003 1004 2001 2002 2003 2004)
+    (iset->list (iset-union (iset 1 2 4 1001 1002)
+                            (iset 1003 1004 2001 2002 2003 2004))))
+(test '(1 2 3 4 1001 1002 1004 2001 2002 2003 2004)
+    (iset->list (iset-union (iset 1 2 3 4 1001 1002)
+                            (iset 1004 2001 2002 2003 2004))))
+(test '(1 2 3 4 1001 1002 1003 1004 2001 2003 2004)
+    (iset->list (iset-union (iset 1 2 3 4 1001 1002)
+                            (iset 1003 1004 2001 2003 2004))))
 
 (test-end)