diff --git a/osc/util/ar.py b/osc/util/ar.py
index 00bd4b60..51834b30 100644
--- a/osc/util/ar.py
+++ b/osc/util/ar.py
@@ -160,9 +160,9 @@ class Ar:
             self.__file = open(self.filename, 'rb')
             try:
                 if sys.platform[:3] != 'win':
-                    self.__file = mmap.mmap(self.__file.fileno(), 0, prot=mmap.PROT_READ)
+                    self.__file = mmap.mmap(self.__file.fileno(), os.path.getsize(self.__file.name), prot=mmap.PROT_READ)
                 else:
-                    self.__file = mmap.mmap(self.__file.fileno(), 0)
+                    self.__file = mmap.mmap(self.__file.fileno(), os.path.getsize(self.__file.name))
             except EnvironmentError, e:
                 if e.errno == 19 or ( hasattr(e, 'winerror') and e.winerror == 5 ):
                     print >>sys.stderr, 'cannot use mmap to read the file, falling back to the default io'
diff --git a/osc/util/cpio.py b/osc/util/cpio.py
index a486942c..35cae47c 100644
--- a/osc/util/cpio.py
+++ b/osc/util/cpio.py
@@ -145,9 +145,9 @@ class CpioRead:
             self.__file = open(self.filename, 'rb')
             try:
                 if sys.platform[:3] != 'win':
-                    self.__file = mmap.mmap(self.__file.fileno(), 0, prot = mmap.PROT_READ)
+                    self.__file = mmap.mmap(self.__file.fileno(), os.path.getsize(self.__file.name), prot = mmap.PROT_READ)
                 else:
-                    self.__file = mmap.mmap(self.__file.fileno(), 0)
+                    self.__file = mmap.mmap(self.__file.fileno(), os.path.getsize(self.__file.name))
             except EnvironmentError, e:
                 if e.errno == 19 or ( hasattr(e, 'winerror') and e.winerror == 5 ):
                     print >>sys.stderr, 'cannot use mmap to read the file, failing back to default'