diff --git a/py_rql/parser.py b/py_rql/parser.py
index 0d993e1..9ed972d 100644
--- a/py_rql/parser.py
+++ b/py_rql/parser.py
@@ -2,6 +2,8 @@
 #  Copyright © 2022 Ingram Micro Inc. All rights reserved.
 #
 
+from threading import Lock
+
 from cachetools import LFUCache
 from lark import Lark
 from lark.exceptions import LarkError
@@ -15,17 +17,23 @@ def __init__(self, *args, **kwargs):
         super(RQLLarkParser, self).__init__(*args, **kwargs)
 
         self._cache = LFUCache(maxsize=1000)
+        self._lock = Lock()
 
     def parse_query(self, query):
         cache_key = hash(query)
-        if cache_key in self._cache:
-            return self._cache[cache_key]
+
         try:
-            rql_ast = self.parse(query)
-            self._cache[cache_key] = rql_ast
-            return rql_ast
-        except LarkError:
-            raise RQLFilterParsingError()
+            return self._cache[cache_key]
+        except KeyError:
+
+            try:
+                rql_ast = self.parse(query)
+                with self._lock:
+                    self._cache[cache_key] = rql_ast
+
+                return rql_ast
+            except LarkError:
+                raise RQLFilterParsingError()
 
 
 RQLParser = RQLLarkParser(RQL_GRAMMAR, parser='lalr', start='start')
diff --git a/tests/test_init.py b/tests/test_init.py
index e2956b7..0c06b0c 100644
--- a/tests/test_init.py
+++ b/tests/test_init.py
@@ -1,11 +1,17 @@
 #
 #  Copyright © 2022 Ingram Micro Inc. All rights reserved.
 #
+import time
+from threading import Thread
+
 import pytest
+from cachetools import LFUCache
 from lark import Tree
 
 from py_rql import parse
 from py_rql.exceptions import RQLFilterParsingError
+from py_rql.grammar import RQL_GRAMMAR
+from py_rql.parser import RQLLarkParser
 
 
 def test_parse_ok():
@@ -15,3 +21,40 @@ def test_parse_ok():
 def test_parse_fail():
     with pytest.raises(RQLFilterParsingError):
         parse('a=')
+
+
+def test_parse_locks():
+    class Cache(LFUCache):
+        def pop(self, key):
+            time.sleep(0.5)
+
+            return super().pop(key)
+
+    cache = Cache(maxsize=1)
+    parser = RQLLarkParser(RQL_GRAMMAR, parser='lalr', start='start')
+    parser._cache = cache
+    parser.parse_query('a=b')
+
+    def func1():
+        parser.parse_query('b=c')
+
+    has_exception = False
+
+    def func2():
+        nonlocal has_exception
+
+        try:
+            parser.parse_query('c=d')
+        except KeyError:
+            has_exception = True
+
+    t1 = Thread(target=func1)
+    t2 = Thread(target=func2)
+
+    t1.start()
+    t2.start()
+    t1.join()
+    t2.join()
+
+    assert not has_exception
+    assert hash('c=d') in cache