diff --git a/docs/release_notes.md b/docs/release_notes.md
index e1840bd1..202bde6d 100644
--- a/docs/release_notes.md
+++ b/docs/release_notes.md
@@ -2,6 +2,11 @@
 
 ## 0.3.0b1 (unreleased)
 
+Constructor signature errors now identify an unexpected keyword in the primary
+`SignatureError` message and `slot`, including through `Definition(...).build()`.
+The stable `"argument binding failed"` reason and original exception cause are
+retained; argument values are not rendered. See [Signatures](signatures.md#errors).
+
 Maintained dense CPU estimator adapters now provide XGBoost classification and
 scalar regression (`dryml.models.xgb`) and statsmodels OLS/binary Logit
 (`dryml.models.statsmodels`). Imports and configuration are passive; fitting and
diff --git a/docs/signatures.md b/docs/signatures.md
index 31a11581..bafeca86 100644
--- a/docs/signatures.md
+++ b/docs/signatures.md
@@ -293,6 +293,14 @@ binding, discovery, context ownership, wrapper conflicts, and unavailable or
 ambiguous authority. Repo and lifecycle errors retain their own types and cleanup
 semantics during Mat realization.
 
+For a closed constructor signature, a known unexpected keyword is included in
+`SignatureError.slot` and the primary message, including through
+`Definition(...).build()`. For example, a misspelled `chlid` keyword reports
+`Signature normalization failed: argument binding failed at chlid.` The reason
+remains `"argument binding failed"`, argument values are excluded, and the
+original Python `TypeError` remains the chained cause. Accepted variadic keyword
+names are not labeled as unexpected when another binding requirement fails.
+
 Symbolic Definition failures use `ParameterizationError(ValueError)`. Its
 specializations are `UnresolvedDefinitionError` for required resolution,
 `ParameterizationLimitError` for bounded traversal or generation work, and
diff --git a/src/dryml/core/signatures.py b/src/dryml/core/signatures.py
index b3cbf223..fa998256 100644
--- a/src/dryml/core/signatures.py
+++ b/src/dryml/core/signatures.py
@@ -29,7 +29,8 @@ class SignatureError(TypeError):
 
     Args:
         reason: Fixed diagnostic category describing the failed contract.
-        slot: Optional parameter or return slot path.
+        slot: Optional parameter or return slot path, including a known
+            unexpected keyword name when binding a closed constructor signature.
 
     Errors never include caller value representations. Chained lower-level errors
     remain available as causes.
@@ -547,6 +548,8 @@ def prepare_args(self, args: tuple[Any, ...], kwargs: Mapping[str, Any], *, repo
 
         Raises:
             SignatureError: If binding, controls, or assertions are invalid.
+                Unexpected keywords in closed constructor signatures identify
+                the keyword in the error's slot without rendering its value.
             Exception: Propagates explicitly requested Repo metadata failures
                 without changing their type.
 
@@ -566,7 +569,16 @@ def _prepare_args(self, args: tuple[Any, ...], kwargs: Mapping[str, Any],
             bound = self.signature.bind(*args, **dict(kwargs))
             bound.apply_defaults()
         except TypeError as error:
-            raise SignatureError("argument binding failed") from error
+            slot = None
+            if self.constructor and not any(
+                parameter.kind is inspect.Parameter.VAR_KEYWORD
+                for parameter in self.signature.parameters.values()
+            ):
+                slot = next((
+                    name for name in kwargs
+                    if type(name) is str and name not in self.signature.parameters
+                ), None)
+            raise SignatureError("argument binding failed", slot) from error
         controls = _validate_controls(
             controls, _selection_keys(self.signature, bound.arguments)
         )
diff --git a/tests/core/test_signatures.py b/tests/core/test_signatures.py
index fc7220aa..20158fee 100644
--- a/tests/core/test_signatures.py
+++ b/tests/core/test_signatures.py
@@ -105,6 +105,64 @@ def __init__(self, value: Ref[ConcreteDefinition]):
     assert compile_signature(ConstructorTarget, constructor=True).slots["value"].role == "ref"
 
 
+def test_definition_build_names_unexpected_constructor_keyword_without_values() -> None:
+    """Definition builds expose the typo in the primary error before construction."""
+
+    with pytest.raises(SignatureError) as caught:
+        Definition(SignatureContainer, child=None, chlid="private argument value").build()
+
+    assert caught.value.reason == "argument binding failed"
+    assert caught.value.slot == "chlid"
+    assert "at chlid" in str(caught.value)
+    assert "private argument value" not in str(caught.value)
+    assert isinstance(caught.value.__cause__, TypeError)
+    assert "chlid" in str(caught.value.__cause__)
+
+
+def test_constructor_keyword_diagnostic_does_not_render_argument_values() -> None:
+    """Finding a constructor typo never invokes a rejected value's repr hook."""
+
+    class Unprintable:
+        def __repr__(self):
+            pytest.fail("binding diagnostics must not render argument values")
+
+    plan = compile_signature(SignatureContainer, constructor=True)
+    with pytest.raises(SignatureError) as caught:
+        plan.prepare_args((), {"child": None, "chlid": Unprintable()})
+
+    assert caught.value.slot == "chlid"
+    assert "at chlid" in str(caught.value)
+
+
+@pytest.mark.parametrize("mode", ("function", "variadic-constructor", "nonstring-key"))
+def test_binding_errors_do_not_guess_unexpected_constructor_keywords(mode) -> None:
+    """Function calls, accepted variadic keys and malformed keys keep generic errors."""
+
+    def target(child=None):
+        return child
+
+    class VariadicConstructor:
+        def __init__(self, required, **options):
+            pytest.fail("invalid calls must fail before the constructor runs")
+
+    if mode == "function":
+        plan = compile_signature(target)
+        kwargs = {"chlid": "private argument value"}
+    elif mode == "variadic-constructor":
+        plan = compile_signature(VariadicConstructor, constructor=True)
+        kwargs = {"valid_extra": "private argument value"}
+    else:
+        plan = compile_signature(SignatureContainer, constructor=True)
+        kwargs = {1: "private argument value"}
+
+    with pytest.raises(SignatureError) as caught:
+        plan.prepare_args((), kwargs)
+
+    assert caught.value.reason == "argument binding failed"
+    assert caught.value.slot is None
+    assert str(caught.value) == "Signature normalization failed: argument binding failed."
+
+
 @pytest.mark.parametrize(
     "annotation",
     (