diff --git a/index.js b/index.js
index b7a85d9..67f131f 100644
--- a/index.js
+++ b/index.js
@@ -29,6 +29,10 @@ function toposort(nodes, edges) {
       throw new Error('Cyclic dependency: '+JSON.stringify(node))
     }
 
+    if (!~nodes.indexOf(node)) {
+      throw new Error('Found unknown node. Make sure to provided all involved nodes. Unknown node: '+JSON.stringify(node))
+    }
+
     if (visited[i]) return;
     visited[i] = true
 
diff --git a/test.js b/test.js
index 56a27e3..10a58af 100644
--- a/test.js
+++ b/test.js
@@ -80,6 +80,20 @@ suite.addBatch(
       assert.instanceOf(val, Error)
     }
   }
+, 'unknown nodes in edges':
+  { topic: function() {
+      return toposort.array(['bla']
+      [ ["foo", 'bar']
+      , ["bar", "ron"]
+      , ["john", "bar"]
+      , ["tom", "john"]
+      , ["ron", "tom"]
+      ])
+    }
+  , 'should throw an exception': function(_, val) {
+      assert.instanceOf(val, Error)
+    }
+  }
 , 'triangular dependency':
   { topic: function() {
       /*
@@ -121,4 +135,4 @@ suite.addBatch(
 })
 .run(null, function() {
   (suite.results.broken+suite.results.errored) > 0 && process.exit(1)
-})
\ No newline at end of file
+})