diff --git a/tests/unit/tools/test_tools.py b/tests/unit/tools/test_tools.py
index 292d2eae..eec3c78f 100644
--- a/tests/unit/tools/test_tools.py
+++ b/tests/unit/tools/test_tools.py
@@ -66,4 +66,4 @@ def test_save_invalid_frame():
     try:
         save_video(frames, "tmp.mp4")
     except ValueError as e:
-        assert str(e) == "Frame is not a valid NumPy array with shape (H, W, C)"
+        assert str(e) == "A frame is not a valid NumPy array with shape (H, W, C)"
diff --git a/vision_agent/tools/tools.py b/vision_agent/tools/tools.py
index bc73a9ae..63776be2 100644
--- a/vision_agent/tools/tools.py
+++ b/vision_agent/tools/tools.py
@@ -1847,7 +1847,7 @@ def save_video(
             frame.shape[0] == 0 and frame.shape[1] == 0
         ):
             raise ValueError(
-                "The frame is not a valid NumPy array with shape (H, W, C)"
+                "A frame is not a valid NumPy array with shape (H, W, C)"
             )
 
     if output_video_path is None: