diff --git a/src/lib/common/file.c b/src/lib/common/file.c
index 03f489eb..84e17c8e 100644
--- a/src/lib/common/file.c
+++ b/src/lib/common/file.c
@@ -66,6 +66,7 @@ int
 ef_open(int type, int how)
 {
     struct empfile *ep;
+    struct flock lock;
     int oflags, fd, fsiz, size;
 
     if (ef_check(type) < 0)
@@ -90,6 +91,14 @@ ef_open(int type, int how)
 	return 0;
     }
 
+    lock.l_type = how & EFF_RDONLY ? F_RDLCK : F_WRLCK;
+    lock.l_whence = SEEK_SET;
+    lock.l_start = lock.l_len = 0;
+    if (fcntl(fd, F_SETLK, &lock) == -1) {
+	logerror("Can't lock %s (%s)", ep->file, strerror(errno));
+	return 0;
+    }
+
     /* get file size */
     fsiz = fsize(fd);
     if (fsiz % ep->size) {