diff --git a/python/sglang/srt/model_loader/weight_utils.py b/python/sglang/srt/model_loader/weight_utils.py
index 67156b16d..16babccaf 100644
--- a/python/sglang/srt/model_loader/weight_utils.py
+++ b/python/sglang/srt/model_loader/weight_utils.py
@@ -686,6 +686,16 @@ def filter_duplicate_safetensors_files(
     weight_files_in_index = set()
     for weight_name in weight_map:
         weight_files_in_index.add(os.path.join(hf_folder, weight_map[weight_name]))
+    # Fail fast if the index references shard files that are not on disk (e.g. an
+    # incomplete or interrupted download). Otherwise those shards are silently
+    # dropped and the model loads with uninitialized weights.
+    missing_files = sorted(f for f in weight_files_in_index if not os.path.isfile(f))
+    if missing_files:
+        raise RuntimeError(
+            f"{index_file} references {len(missing_files)} shard file(s) missing "
+            f"from {hf_folder} (incomplete download?): "
+            f"{[os.path.basename(f) for f in missing_files]}"
+        )
     # Filter out any fields that are not found in the index file.
     hf_weights_files = [f for f in hf_weights_files if f in weight_files_in_index]
     return hf_weights_files
diff --git a/test/registered/unit/model_loader/test_weight_utils.py b/test/registered/unit/model_loader/test_weight_utils.py
new file mode 100644
index 000000000..0e4ba5ed0
--- /dev/null
+++ b/test/registered/unit/model_loader/test_weight_utils.py
@@ -0,0 +1,88 @@
+"""Unit tests for srt/model_loader/weight_utils.py shard-index consistency."""
+
+import json
+import os
+import tempfile
+import unittest
+
+from sglang.srt.model_loader.weight_utils import filter_duplicate_safetensors_files
+from sglang.test.ci.ci_register import register_cpu_ci
+from sglang.test.test_utils import CustomTestCase
+
+register_cpu_ci(est_time=5, suite="base-a-test-cpu")
+
+INDEX_NAME = "model.safetensors.index.json"
+
+
+def _write_index(folder, weight_map):
+    with open(os.path.join(folder, INDEX_NAME), "w") as f:
+        json.dump({"weight_map": weight_map}, f)
+
+
+def _touch(folder, name):
+    path = os.path.join(folder, name)
+    open(path, "w").close()
+    return path
+
+
+class TestFilterDuplicateSafetensorsFiles(CustomTestCase):
+    def setUp(self):
+        self._tmp = tempfile.TemporaryDirectory()
+        self.folder = self._tmp.name
+
+    def tearDown(self):
+        self._tmp.cleanup()
+
+    def test_missing_shard_raises(self):
+        # Index lists two shards, only one on disk (interrupted download).
+        _write_index(
+            self.folder,
+            {
+                "w1": "model-00001-of-00002.safetensors",
+                "w2": "model-00002-of-00002.safetensors",
+            },
+        )
+        present = _touch(self.folder, "model-00001-of-00002.safetensors")
+
+        with self.assertRaises(RuntimeError) as cm:
+            filter_duplicate_safetensors_files(
+                hf_weights_files=[present],
+                hf_folder=self.folder,
+                index_file=INDEX_NAME,
+            )
+        self.assertIn("model-00002-of-00002.safetensors", str(cm.exception))
+
+    def test_complete_checkpoint_filters_non_indexed(self):
+        # All indexed shards present; a non-indexed duplicate is still filtered out.
+        _write_index(
+            self.folder,
+            {
+                "w1": "model-00001-of-00002.safetensors",
+                "w2": "model-00002-of-00002.safetensors",
+            },
+        )
+        shard1 = _touch(self.folder, "model-00001-of-00002.safetensors")
+        shard2 = _touch(self.folder, "model-00002-of-00002.safetensors")
+        extra = _touch(self.folder, "consolidated.safetensors")
+
+        result = filter_duplicate_safetensors_files(
+            hf_weights_files=[shard1, shard2, extra],
+            hf_folder=self.folder,
+            index_file=INDEX_NAME,
+        )
+        self.assertEqual(sorted(result), sorted([shard1, shard2]))
+
+    def test_single_file_model_no_index_returns_unchanged(self):
+        # No index on disk (single-file / dummy / object-storage): early return.
+        single = _touch(self.folder, "model.safetensors")
+
+        result = filter_duplicate_safetensors_files(
+            hf_weights_files=[single],
+            hf_folder=self.folder,
+            index_file=INDEX_NAME,
+        )
+        self.assertEqual(result, [single])
+
+
+if __name__ == "__main__":
+    unittest.main()