Index: wafadmin/Scan.py
===================================================================
--- wafadmin/Scan.py	(revision 1327)
+++ wafadmin/Scan.py	(working copy)
@@ -94,7 +94,12 @@
 			for dep in lst:
 				if not dep.m_name in seen:
 					add_node_sig(dep)
-			m.update(tree.m_tstamp_variants[variant][node])
+			try:
+				m.update(tree.m_tstamp_variants[variant][node])
+			except KeyError:
+				sig = Params.h_file(node.bldpath(env))
+				tree.m_tstamp_variants[variant][node] = sig
+				m.update(sig)
 
 		# add the signatures of the input nodes
 		for node in task.m_inputs: add_node_sig(node)