diff --git a/src/libutil/archive.cc b/src/libutil/archive.cc
index 8f100da4c..4899fbaa4 100644
--- a/src/libutil/archive.cc
+++ b/src/libutil/archive.cc
@@ -181,6 +181,8 @@ static void parseContents(ParseSink & sink, Source & source, const Path & path)
         left -= n;
     }
 
+    sink.finalizeContents(size);
+
     readPadding(size, source);
 }
 
@@ -310,6 +312,12 @@ struct RestoreSink : ParseSink
         writeFull(fd, data, len);
     }
 
+    void finalizeContents(unsigned long long size)
+    {
+        errno = ftruncate(fd, size);
+        if (errno) throw SysError(format("truncating file to its allocated length of %1% bytes") % size);
+    }
+
     void createSymlink(const Path & path, const string & target)
     {
         Path p = dstPath + path;
diff --git a/src/libutil/archive.hh b/src/libutil/archive.hh
index fff620313..f358a2a6b 100644
--- a/src/libutil/archive.hh
+++ b/src/libutil/archive.hh
@@ -64,6 +64,7 @@ struct ParseSink
     virtual void isExecutable() { };
     virtual void preallocateContents(unsigned long long size) { };
     virtual void receiveContents(unsigned char * data, unsigned int len) { };
+    virtual void finalizeContents(unsigned long long size) { };
 
     virtual void createSymlink(const Path & path, const string & target) { };
 };