diff --git a/changelog.d/3350-uniqueness-scope-guard.fixed.md b/changelog.d/3350-uniqueness-scope-guard.fixed.md
new file mode 100644
index 000000000..a6e6cb380
--- /dev/null
+++ b/changelog.d/3350-uniqueness-scope-guard.fixed.md
@@ -0,0 +1 @@
+- `validatesUniquenessOf(property="x", scope="y")` now returns a validation result instead of throwing `Component [Model] has no accessible Member with name [y]` when the scope property was never assigned. Building the uniqueness `WHERE` clause dereferenced every scope property without an existence guard, and a scope property is easy to leave absent rather than empty: `$setDefaultValues()` only seeds properties with an explicit `property()` mapping, so a column with a database-level default but no mapping is missing from a `new()`-ed object entirely. An absent scope property is now treated as blank, matching what a present-but-empty one has always done — including the existing conversion of an empty numeric scope to `IS NULL`. The `property(name="<scopeProperty>", defaultValue="")` workaround is no longer needed (#3350)
diff --git a/vendor/wheels/model/validations.cfc b/vendor/wheels/model/validations.cfc
index cfd0ff5df..b1dffdeba 100644
--- a/vendor/wheels/model/validations.cfc
+++ b/vendor/wheels/model/validations.cfc
@@ -783,8 +783,18 @@ component {
 	 * and converting blank numeric properties to IS NULL.
 	 */
 	public string function $buildWhereClausePart(required string property) {
+		// A property named in `scope=` may be absent rather than empty: `$setDefaultValues()`
+		// only seeds properties with an explicit `property()` mapping, so a column that has a
+		// database-level default but no mapping never appears on a `new()`-ed object. Reading
+		// it unguarded threw "has no accessible Member" out of a validation, so an absent
+		// scope property produced an exception where a blank one produced a validation result
+		// (issue #3350). The validated property itself cannot be absent here —
+		// `$shouldInvokeValidation()` skips the validation in that case — so this guard only
+		// ever fires for scopes. Treat absent as blank, which is the branch below that turns
+		// an empty numeric into `IS NULL`.
+		local.value = StructKeyExists(this, arguments.property) ? this[arguments.property] : "";
 		local.part = arguments.property & "=" & variables.wheels.class.adapter.$quoteValue(
-			str = this[arguments.property],
+			str = local.value,
 			type = validationTypeForProperty(arguments.property)
 		);
 		if (Right(local.part, 3) == "=''" && ListFindNoCase("integer,float,boolean", validationTypeForProperty(arguments.property))) {
diff --git a/vendor/wheels/tests/specs/model/validationsSpec.cfc b/vendor/wheels/tests/specs/model/validationsSpec.cfc
index 6dfdc974d..1d9684313 100644
--- a/vendor/wheels/tests/specs/model/validationsSpec.cfc
+++ b/vendor/wheels/tests/specs/model/validationsSpec.cfc
@@ -1015,6 +1015,32 @@ component extends="wheels.WheelsTest" {
 				expect(combiKey.valid()).toBeFalse()
 			})
 
+			// Issue #3350: a property named in `scope=` that was never assigned is ABSENT
+			// from the object, not present-and-empty — `$setDefaultValues()` only seeds
+			// properties with an explicit `property()` mapping. The scope dereference had no
+			// existence guard, so building the uniqueness WHERE clause threw
+			// "Component [X] has no accessible Member with name [Y]" out of a method whose
+			// entire job is to return a validation result. The validated property itself
+			// cannot hit this — `$shouldInvokeValidation()` skips the validation when it is
+			// absent — so only `scope=` was exposed.
+			it("validatesUniquenessOf_with_absent_scope_property", () => {
+				combiKey = g.model("combiKey").new(id1 = 1, id2 = 1)
+				StructDelete(combiKey, "id2")
+
+				// must return a validation result rather than throwing
+				expect(combiKey.valid()).toBeFalse()
+			})
+
+			// An absent scope property must behave exactly like a present-but-empty one —
+			// the split between the two was the defect, not the value itself.
+			it("validatesUniquenessOf_absent_scope_matches_blank_scope", () => {
+				absent = g.model("combiKey").new(id1 = 1, id2 = "")
+				StructDelete(absent, "id2")
+				blank = g.model("combiKey").new(id1 = 1, id2 = "")
+
+				expect(absent.$buildWhereClausePart("id2")).toBe(blank.$buildWhereClausePart("id2"))
+			})
+
 			it("validatesUniquenessOf_with_blank_property_value", () => {
 				user.blank = ""
 				user.validatesUniquenessOf(properties = "blank")