diff --git a/chapter2/2.10.scm b/chapter2/2.10.scm
index 7c519ea..fc56272 100644
--- a/chapter2/2.10.scm
+++ b/chapter2/2.10.scm
@@ -17,9 +17,9 @@
                    (max p1 p2 p3 p4))))
 
 (define (div-interval x y)
-  (if (= (upper-bound y)
-         (lower-bound y))
-      (error "Division by zero")
-      (mul-interval x
-                    (make-interval (/ 1.0 (upper-bound y))
-                                   (/ 1.0 (lower-bound y))))))
+  (if (> (* (lower-bound y) 
+            (upper-bound y)) 0)
+  (mul-interval x 
+                (make-interval (/ 1.0 (upper-bound y))
+                               (/ 1.0 (lower-bound y))))
+  (error "Division by an interval spanning zero")))