diff --git a/sagemaker-train/src/sagemaker/train/utils.py b/sagemaker-train/src/sagemaker/train/utils.py
index 31d26daecd..bd82835294 100644
--- a/sagemaker-train/src/sagemaker/train/utils.py
+++ b/sagemaker-train/src/sagemaker/train/utils.py
@@ -137,9 +137,9 @@ def _get_unique_name(base, max_length=63):
         str: The unique name
     """
     current_time = datetime.now().strftime("%Y%m%d%H%M%S")
-    base = base.replace("_", "-")
+    # Truncate the base, not the timestamp, so the name stays unique
+    base = base.replace("_", "-")[: max_length - len(current_time) - 1]
     unique_name = f"{base}-{current_time}"
-    unique_name = unique_name[:max_length]  # Truncate to max_length
     return unique_name
 
 
diff --git a/sagemaker-train/tests/unit/train/test_model_trainer.py b/sagemaker-train/tests/unit/train/test_model_trainer.py
index 18d0f8a299..c78bf67441 100644
--- a/sagemaker-train/tests/unit/train/test_model_trainer.py
+++ b/sagemaker-train/tests/unit/train/test_model_trainer.py
@@ -2774,3 +2774,14 @@ def test_pipeline_and_interactive_emit_identical_tags(model_trainer):
     pipeline_tags = _pipeline_trainer([TAG])._create_training_job_args()["Tags"]
 
     assert pipeline_tags == _train_wire_tags(model_trainer)
+
+
+@patch("sagemaker.train.utils.datetime")
+def test_get_unique_name_keeps_timestamp_for_long_base_name(mock_datetime):
+    from datetime import datetime
+
+    from sagemaker.train.utils import _get_unique_name
+
+    mock_datetime.now.return_value = datetime(2026, 9, 26, 12, 34, 56)
+
+    assert _get_unique_name("a" * 60) == "a" * 48 + "-20260926123456"