diff --git a/openevolve/database.py b/openevolve/database.py
index 8abe2bdc0..4cd50166f 100644
--- a/openevolve/database.py
+++ b/openevolve/database.py
@@ -1045,8 +1045,9 @@ def _llm_judge_novelty(self, program: Program, similar_program: Program) -> bool
             content = content.strip()
 
             # Parse the response
-            NOVEL_i = content.upper().find("NOVEL")
-            NOT_NOVEL_i = content.upper().find("NOT NOVEL")
+            parsed_content = content.upper().replace("NOT_NOVEL", "NOT NOVEL")
+            NOVEL_i = parsed_content.find("NOVEL")
+            NOT_NOVEL_i = parsed_content.find("NOT NOVEL")
 
             if NOVEL_i == -1 and NOT_NOVEL_i == -1:
                 logger.warning(f"Unexpected novelty LLM response: {content}")
diff --git a/tests/test_novelty_response_parsing.py b/tests/test_novelty_response_parsing.py
new file mode 100644
index 000000000..5e9d5b14d
--- /dev/null
+++ b/tests/test_novelty_response_parsing.py
@@ -0,0 +1,47 @@
+"""Tests for parsing responses from the LLM novelty judge."""
+
+import unittest
+
+from openevolve.config import Config
+from openevolve.database import Program, ProgramDatabase
+
+
+class MockNoveltyLLM:
+    def __init__(self, response: str):
+        self.response = response
+
+    async def generate_with_context(self, system_message: str, messages: list) -> str:
+        return self.response
+
+
+class TestNoveltyResponseParsing(unittest.TestCase):
+    def setUp(self) -> None:
+        config = Config()
+        config.database.in_memory = True
+        config.database.novelty_llm = MockNoveltyLLM("NOVEL")
+        self.db = ProgramDatabase(config.database)
+        self.existing_program = Program(id="existing", code="return 1")
+        self.proposed_program = Program(id="proposed", code="return 2")
+
+    def judge(self, response: str) -> bool:
+        self.db.novelty_llm = MockNoveltyLLM(response)
+        return self.db._llm_judge_novelty(self.proposed_program, self.existing_program)
+
+    def test_prompted_not_novel_responses_are_rejected(self) -> None:
+        responses = [
+            "NOT_NOVEL",
+            "NOT_NOVEL: the programs are equivalent",
+            "**NOT_NOVEL**",
+            "NOT NOVEL",
+        ]
+
+        for response in responses:
+            with self.subTest(response=response):
+                self.assertFalse(self.judge(response))
+
+    def test_novel_response_is_accepted(self) -> None:
+        self.assertTrue(self.judge("NOVEL: the programs behave differently"))
+
+
+if __name__ == "__main__":
+    unittest.main()