diff --git a/src/main/kotlin/com/beust/kobalt/misc/Topological.kt b/src/main/kotlin/com/beust/kobalt/misc/Topological.kt
index 0b65dc75..0003b4a4 100644
--- a/src/main/kotlin/com/beust/kobalt/misc/Topological.kt
+++ b/src/main/kotlin/com/beust/kobalt/misc/Topological.kt
@@ -1,5 +1,6 @@
 package com.beust.kobalt.misc
 
+import com.beust.kobalt.KobaltException
 import com.google.common.collect.ArrayListMultimap
 import com.google.common.collect.HashMultimap
 import java.util.*
@@ -29,6 +30,9 @@ class Topological<T> {
             val freeNodes = all.filter {
                 dependMap.get(it).isEmpty()
             }
+            if (freeNodes.isEmpty()) {
+                throw KobaltException("The dependency graph has a cycle: $all")
+            }
             result.addAll(freeNodes)
             all.removeAll(freeNodes)
             val newMap = HashMultimap.create<T, T>()