diff --git a/packages/quicktype-core/src/rewrites/ResolveIntersections.ts b/packages/quicktype-core/src/rewrites/ResolveIntersections.ts
index 05b424f43..12aea46c2 100644
--- a/packages/quicktype-core/src/rewrites/ResolveIntersections.ts
+++ b/packages/quicktype-core/src/rewrites/ResolveIntersections.ts
@@ -183,6 +183,9 @@ class IntersectionAccumulator
             return;
         }
 
+        // Named properties from intersected objects are combined.  Whether
+        // additional properties are allowed only affects names not declared
+        // by any of those objects.
         const allPropertyNames = setUnionInto(
             new Set(this._objectProperties.keys()),
             maybeObject.getProperties().keys(),
diff --git a/test/inputs/schema/allof-closed-objects.1.fail.no-defaults.json b/test/inputs/schema/allof-closed-objects.1.fail.no-defaults.json
new file mode 100644
index 000000000..a145c7895
--- /dev/null
+++ b/test/inputs/schema/allof-closed-objects.1.fail.no-defaults.json
@@ -0,0 +1,6 @@
+{
+  "animal": {
+    "foo": "inherited property",
+    "bar": "inline property"
+  }
+}
diff --git a/test/inputs/schema/allof-closed-objects.1.json b/test/inputs/schema/allof-closed-objects.1.json
new file mode 100644
index 000000000..a5e433dd2
--- /dev/null
+++ b/test/inputs/schema/allof-closed-objects.1.json
@@ -0,0 +1,7 @@
+{
+  "animal": {
+    "foo": "inherited property",
+    "discriminator": "dog",
+    "bar": "inline property"
+  }
+}
diff --git a/test/inputs/schema/allof-closed-objects.schema b/test/inputs/schema/allof-closed-objects.schema
new file mode 100644
index 000000000..35727a276
--- /dev/null
+++ b/test/inputs/schema/allof-closed-objects.schema
@@ -0,0 +1,37 @@
+{
+  "$schema": "http://json-schema.org/draft-04/schema#",
+  "title": "Container",
+  "type": "object",
+  "additionalProperties": false,
+  "properties": {
+    "animal": {
+      "oneOf": [
+        { "$ref": "#/definitions/dog" },
+        { "type": "null" }
+      ]
+    }
+  },
+  "definitions": {
+    "dog": {
+      "allOf": [
+        { "$ref": "#/definitions/animal" },
+        {
+          "type": "object",
+          "additionalProperties": false,
+          "properties": {
+            "bar": { "type": ["null", "string"] }
+          }
+        }
+      ]
+    },
+    "animal": {
+      "type": "object",
+      "additionalProperties": false,
+      "required": ["discriminator"],
+      "properties": {
+        "foo": { "type": ["null", "string"] },
+        "discriminator": { "type": "string" }
+      }
+    }
+  }
+}
diff --git a/test/languages.ts b/test/languages.ts
index 120f3170b..1a68ffd4f 100644
--- a/test/languages.ts
+++ b/test/languages.ts
@@ -678,6 +678,7 @@ export const CJSONLanguage: Language = {
         /* Required properties absent are not checked (for the current implementation, can be added later, should abord parsing and return NULL) */
         "intersection.schema",
         "required.schema",
+        "allof-closed-objects.schema",
         // The default-value fail sample also relies on required-property
         // enforcement, which cJSON does not do.
         "default-value.schema",
@@ -1002,6 +1003,8 @@ export const SwiftLanguage: Language = {
         // This works on macOS, but on Linux one of the failure test cases doesn't fail
         ...skipsUntypedUnions,
         "required.schema",
+        // Same Linux-only missing-required behavior as required.schema.
+        "allof-closed-objects.schema",
         // The default-value fail sample also relies on required-property enforcement.
         "default-value.schema",
         "multi-type-enum.schema",
@@ -1918,6 +1921,9 @@ export const HaskellLanguage: Language = {
         "keyword-unions.schema",
         "optional-any.schema",
         "required.schema",
+        // Same undetectable expected-failure limitation as required.schema:
+        // a failed decode prints "null" and exits 0.
+        "allof-closed-objects.schema",
         // The default-value fail sample also relies on required-property enforcement.
         "default-value.schema",
         "required-non-properties.schema",
@@ -2273,6 +2279,7 @@ export const ElixirLanguage: Language = {
         // Struct keys cannot be enforced at runtime in Elixir and their values will just be set to null.
         "strict-optional.schema",
         "required.schema",
+        "allof-closed-objects.schema",
         // The default-value fail sample also relies on required-property enforcement.
         "default-value.schema",
         "boolean-subschema.schema",