diff --git a/lbuild/ruletable.lua b/lbuild/ruletable.lua
index 362101a..4a1a6e4 100644
--- a/lbuild/ruletable.lua
+++ b/lbuild/ruletable.lua
@@ -169,4 +169,15 @@ ruletable:addgenerator(function(name)
     return nil
 end)
 
+runner.ondeadlock = function()
+    print("Deadlock!")
+    print("Incomplete operations:")
+    for i, v in pairs(ruletbl.rules) do
+        if v.state ~= "done" and v.state then
+            print(string.format("\t%s (%s)", i, v.state))
+        end
+    end
+    error("deadlock")
+end
+
 return ruletable
diff --git a/lbuild/runner.lua b/lbuild/runner.lua
index bc3d1fa..5efa600 100644
--- a/lbuild/runner.lua
+++ b/lbuild/runner.lua
@@ -90,6 +90,9 @@ function runner:wait()
         op.pid = nil
         self.n = self.n - 1
     else
+        if runner.ondeadlock then
+            runner.ondeadlock()
+        end
         error("Nothing running")
     end
 end