diff --git a/src/main/java/org/boris/expr/util/Graph.java b/src/main/java/org/boris/expr/util/Graph.java
index cc7b839..a5fe31a 100644
--- a/src/main/java/org/boris/expr/util/Graph.java
+++ b/src/main/java/org/boris/expr/util/Graph.java
@@ -56,8 +56,11 @@ public void clearInbounds(Object node) {
         Set s = (Set) inbounds.get(node);
         if (s != null) {
             Iterator i = s.iterator();
+            Set<Edge> remove = new HashSet<Edge>();
             while (i.hasNext())
-                remove((Edge) i.next());
+                remove.add((Edge) i.next());
+            for (Edge edge : remove)
+                remove(edge);
         }
     }
 
diff --git a/src/test/java/org/boris/expr/DependencyEngineTest.java b/src/test/java/org/boris/expr/DependencyEngineTest.java
index 36925a6..6fc5ee3 100644
--- a/src/test/java/org/boris/expr/DependencyEngineTest.java
+++ b/src/test/java/org/boris/expr/DependencyEngineTest.java
@@ -34,6 +34,7 @@ public void testRangeDependencies() throws Exception {
         e.set("B1", "2");
         e.set("A2", "3");
         e.set("B2", "4");
+        e.set("D4", "=sum(A1:A2)");
         e.set("D4", "=sum(A1:B2)");
         assertResult(e, "D4", 10);
         e.set("A1", "10");