diff --git a/tools/Polygraphy/CHANGELOG.md b/tools/Polygraphy/CHANGELOG.md
index cea3567e..542e3937 100644
--- a/tools/Polygraphy/CHANGELOG.md
+++ b/tools/Polygraphy/CHANGELOG.md
@@ -3,6 +3,12 @@
 Dates are in YYYY-MM-DD format.
 
 
+## Unreleased
+### Fixed
+- Parsing a tensor shape no longer accepts a missing, extra, or reversed bracket.
+  `input:[1,2` was read as shape `[1, 2]`.
+
+
 ## v0.53.6 (2026-09-22)
 ### Added
 - `Comparator.run()` now accepts a `save_input_blob_path` parameter, exposed on the CLI as
diff --git a/tools/Polygraphy/polygraphy/tools/args/util/util.py b/tools/Polygraphy/polygraphy/tools/args/util/util.py
index 0ace0371..6c0ca37b 100644
--- a/tools/Polygraphy/polygraphy/tools/args/util/util.py
+++ b/tools/Polygraphy/polygraphy/tools/args/util/util.py
@@ -38,8 +38,17 @@ def cast(val):
     """
     val = str(val.strip())
 
-    if val.strip("[]") != val:
-        return [cast(elem) for elem in val.strip("[]").split(",")]
+    if "[" in val or "]" in val:
+        well_formed = val.startswith("[") and val.endswith("]")
+        inner = val[1:-1] if well_formed else ""
+        if not well_formed or "[" in inner or "]" in inner:
+            G_LOGGER.critical(
+                f"Could not parse {val} as a list. "
+                "Lists must start with '[' and end with ']', with no other brackets."
+            )
+        if not inner.strip():
+            return []
+        return [cast(elem) for elem in inner.split(",")]
 
     try:
         return int(val)  # This fails for float strings like '0.0'
diff --git a/tools/Polygraphy/tests/tools/args/util/test_util.py b/tools/Polygraphy/tests/tools/args/util/test_util.py
index c43def4c..2a8f6855 100644
--- a/tools/Polygraphy/tests/tools/args/util/test_util.py
+++ b/tools/Polygraphy/tests/tools/args/util/test_util.py
@@ -71,6 +71,11 @@ def test_parse_shape_with_dim_param_quoted(self, name, quote):
         meta = args_util.parse_meta(meta_args, includes_dtype=False)
         assert meta[name].shape == ["batch", 3, 224, 224]
 
+    @pytest.mark.parametrize("shape", ["[1,2", "1,2]", "]1,2[", "[1,2]]"])
+    def test_unbalanced_shape_is_rejected(self, name, shape):
+        with pytest.raises(PolygraphyException, match="Could not parse"):
+            args_util.parse_meta([f"{name}:{shape}"], includes_dtype=False)
+
 
 class TestRunScript:
     def test_default_args(self):