diff --git a/pyproject.toml b/pyproject.toml
index ca4cf0e..01630bf 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "FSRS-Optimizer"
-version = "5.2.0"
+version = "5.2.1"
 readme = "README.md"
 dependencies = [
     "matplotlib>=3.7.0",
diff --git a/src/fsrs_optimizer/fsrs_optimizer.py b/src/fsrs_optimizer/fsrs_optimizer.py
index fa5bdd6..2178198 100644
--- a/src/fsrs_optimizer/fsrs_optimizer.py
+++ b/src/fsrs_optimizer/fsrs_optimizer.py
@@ -752,7 +752,11 @@ def create_time_series(
         if df.empty:
             raise ValueError("Training data is inadequate.")
 
-        if "review_state" in df.columns and "review_duration" in df.columns:
+        if (
+            "review_state" in df.columns
+            and "review_duration" in df.columns
+            and not (df["review_duration"] == 0).all()
+        ):
             df["review_state"] = df["review_state"].map(
                 lambda x: x if x != New else Learning
             )