diff --git a/src/client.py b/src/client.py
--- a/src/client.py
+++ b/src/client.py
@@ -8,7 +8,7 @@ import config as conf
 import stats
 from util import Progress
 from hashtree import HashTree,hashBlock
-from netnode import BaseConnection,NetNode,FailedConnection
+from netnode import BaseConnection,NetNode,FailedConnection,LockedException
 
 
 class DeniedConnection(Exception): pass
@@ -125,8 +125,13 @@ class Client(NetNode):
 		log.info("closing session...")
 		dataFile.close()
 
-	def pullData(self,blocksToTransfer):
-		self._lock()
+	def pullData(self,blocksToTransfer,ignoreLock=False):
+		if not ignoreLock:
+			try:
+				self._lock()
+			except LockedException:
+				print("The file is locked. Either (a) there's another pull going on (then wait or kill it), or (b) a previous pull ended prematurely and the file is probably corrupt (then repeat pull with -f for force).")
+				return
 		log.info(blocksToTransfer)
 		dataFile=open(self._filename, mode="rb+")
 		i1=-1