diff --git a/install_lang.py b/install_lang.py
index bbe02c0..80c40ea 100644
--- a/install_lang.py
+++ b/install_lang.py
@@ -36,6 +36,7 @@ if action == 'install':
     fname = fn_dir + filename
     print('Convert file "{}" to LMO ...'.format(fname))
     lmo = po2lmo.Lmo()
+    lmo.skip_dup = True
     lmo.load_from_text(fname)
     lmo_fname = os.path.splitext(filename)[0] + '.lmo'
     lmo.save_to_bin(fn_dir + lmo_fname)
diff --git a/po2lmo.py b/po2lmo.py
index 6c5b175..57f3227 100644
--- a/po2lmo.py
+++ b/po2lmo.py
@@ -102,10 +102,15 @@ class Lmo:
 
   def __init__(self, verbose = 0):
     self.verbose = verbose
+    self.skip_dup = False
     self.entries = []
     self.msg = Msg()
 
   def add_entry(self, key_id, val_id, val):
+    if self.skip_dup:
+      ent = next((ent for ent in self.entries if ent.key_id == key_id), None)
+      if ent:
+        return False  # skip duplicate
     entry = LmoEntry()
     entry.key_id = key_id
     entry.val_id = val_id
@@ -113,6 +118,7 @@ class Lmo:
     entry.length = len(val)
     entry.val = val
     self.entries.append(entry)
+    return True
 
   def print_msg(self):
     msg = self.msg