diff --git a/fixtures/polymorphism.json b/fixtures/polymorphism.json
index 9017f04..3df37bf 100644
--- a/fixtures/polymorphism.json
+++ b/fixtures/polymorphism.json
@@ -636,5 +636,110 @@
         }
       }
     ]
+  },
+  {
+    "description": "STI Projections (Lacking Kind Discriminator Definitions)",
+    "database": {
+      "types": [
+        {
+          "name": "widget",
+          "variations": [
+            "widget"
+          ],
+          "schemas": {
+            "widget": {
+              "type": "object",
+              "properties": {
+                "type": {
+                  "type": "string"
+                }
+              }
+            },
+            "stock.widget": {
+              "type": "widget",
+              "properties": {
+                "kind": {
+                  "type": "string"
+                },
+                "amount": {
+                  "type": "integer"
+                }
+              }
+            },
+            "projected.widget": {
+              "type": "widget",
+              "properties": {
+                "alias": {
+                  "type": "string"
+                }
+              }
+            }
+          }
+        }
+      ],
+      "schemas": {
+        "stock_widget_validation": {
+          "type": "stock.widget"
+        },
+        "projected_widget_validation": {
+          "type": "projected.widget"
+        }
+      }
+    },
+    "tests": [
+      {
+        "description": "stock.widget securely expects kind when configured",
+        "schema_id": "stock_widget_validation",
+        "data": {
+          "type": "widget",
+          "amount": 5
+        },
+        "action": "validate",
+        "expect": {
+          "success": false,
+          "errors": [
+            {
+              "code": "MISSING_KIND",
+              "details": {
+                "path": ""
+              }
+            }
+          ]
+        }
+      },
+      {
+        "description": "projected.widget seamlessly bypasses kind expectation when excluded from schema",
+        "schema_id": "projected_widget_validation",
+        "data": {
+          "type": "widget",
+          "alias": "Test Projection"
+        },
+        "action": "validate",
+        "expect": {
+          "success": true
+        }
+      },
+      {
+        "description": "projected.widget securely fails if user erroneously provides extra kind property",
+        "schema_id": "projected_widget_validation",
+        "data": {
+          "type": "widget",
+          "alias": "Test Projection",
+          "kind": "projected"
+        },
+        "action": "validate",
+        "expect": {
+          "success": false,
+          "errors": [
+            {
+              "code": "STRICT_PROPERTY_VIOLATION",
+              "details": {
+                "path": "kind"
+              }
+            }
+          ]
+        }
+      }
+    ]
   }
 ]
\ No newline at end of file
diff --git a/src/tests/fixtures.rs b/src/tests/fixtures.rs
index 57c65e3..3d06ef4 100644
--- a/src/tests/fixtures.rs
+++ b/src/tests/fixtures.rs
@@ -1559,6 +1559,24 @@ fn test_polymorphism_4_1() {
     crate::tests::runner::run_test_case(&path, 4, 1).unwrap();
 }
 
+#[test]
+fn test_polymorphism_5_0() {
+    let path = format!("{}/fixtures/polymorphism.json", env!("CARGO_MANIFEST_DIR"));
+    crate::tests::runner::run_test_case(&path, 5, 0).unwrap();
+}
+
+#[test]
+fn test_polymorphism_5_1() {
+    let path = format!("{}/fixtures/polymorphism.json", env!("CARGO_MANIFEST_DIR"));
+    crate::tests::runner::run_test_case(&path, 5, 1).unwrap();
+}
+
+#[test]
+fn test_polymorphism_5_2() {
+    let path = format!("{}/fixtures/polymorphism.json", env!("CARGO_MANIFEST_DIR"));
+    crate::tests::runner::run_test_case(&path, 5, 2).unwrap();
+}
+
 #[test]
 fn test_not_0_0() {
     let path = format!("{}/fixtures/not.json", env!("CARGO_MANIFEST_DIR"));
diff --git a/src/validator/rules/extensible.rs b/src/validator/rules/extensible.rs
index bcb0ed3..25cd4dc 100644
--- a/src/validator/rules/extensible.rs
+++ b/src/validator/rules/extensible.rs
@@ -24,9 +24,6 @@ impl<'a> ValidationContext<'a> {
 
     if let Some(obj) = self.instance.as_object() {
       for key in obj.keys() {
-        if key == "type" || key == "kind" {
-          continue; // Reserved keywords implicitly allowed
-        }
         if !result.evaluated_keys.contains(key) && !self.overrides.contains(key) {
           result.errors.push(ValidationError {
             code: "STRICT_PROPERTY_VIOLATION".to_string(),
diff --git a/src/validator/rules/object.rs b/src/validator/rules/object.rs
index cd0ec41..2adfba3 100644
--- a/src/validator/rules/object.rs
+++ b/src/validator/rules/object.rs
@@ -54,14 +54,19 @@ impl<'a> ValidationContext<'a> {
 
           // If the target mathematically declares a horizontal structural STI variation natively
           if schema_identifier_str.contains('.') {
-            if obj.get("kind").is_none() {
-              result.errors.push(ValidationError {
-                code: "MISSING_KIND".to_string(),
-                message: "Schema mechanically requires horizontal kind discrimination".to_string(),
-                path: self.path.clone(),
-              });
-            } else {
-              result.evaluated_keys.insert("kind".to_string());
+            let requires_kind = self.schema.compiled_properties.get()
+                .map_or(false, |p| p.contains_key("kind"));
+            
+            if requires_kind {
+              if obj.get("kind").is_none() {
+                result.errors.push(ValidationError {
+                  code: "MISSING_KIND".to_string(),
+                  message: "Schema mechanically requires horizontal kind discrimination".to_string(),
+                  path: self.path.clone(),
+                });
+              } else {
+                result.evaluated_keys.insert("kind".to_string());
+              }
             }
           }
         } else {