diff --git a/tslang/test/tester/CMakeLists.txt b/tslang/test/tester/CMakeLists.txt
index e9e799b6e..70a2e5d53 100644
--- a/tslang/test/tester/CMakeLists.txt
+++ b/tslang/test/tester/CMakeLists.txt
@@ -418,6 +418,7 @@ tslang_add_test(NAME test-compile-00-nullable-class-to-interface COMMAND test-ru
 tslang_add_test(NAME test-compile-00-class-to-interface-null COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00class_to_interface_null.ts")
 tslang_add_test(NAME test-compile-00-null-interface-to-interface COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00null_interface_to_interface.ts")
 tslang_add_test(NAME test-compile-00-interface-type-tag-in-vtable COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00interface_type_tag_in_vtable.ts")
+tslang_add_test(NAME test-compile-00-nullable-interface-to-interface COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00nullable_interface_to_interface.ts")
 tslang_add_test(NAME test-compile-00-argument-place-aliased COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00argument_place_aliased.ts")
 tslang_add_test(NAME test-compile-00-temporary-read-in-finally COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00temporary_read_in_finally.ts")
 tslang_add_test(NAME test-compile-00-unowned-local-store COMMAND test-runner "${PROJECT_SOURCE_DIR}/test/tester/tests/00unowned_local_store.ts")
@@ -1015,6 +1016,7 @@ tslang_add_test(NAME test-jit-00-nullable-class-to-interface COMMAND test-runner
 tslang_add_test(NAME test-jit-00-class-to-interface-null COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00class_to_interface_null.ts")
 tslang_add_test(NAME test-jit-00-null-interface-to-interface COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00null_interface_to_interface.ts")
 tslang_add_test(NAME test-jit-00-interface-type-tag-in-vtable COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00interface_type_tag_in_vtable.ts")
+tslang_add_test(NAME test-jit-00-nullable-interface-to-interface COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00nullable_interface_to_interface.ts")
 tslang_add_test(NAME test-jit-00-argument-place-aliased COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00argument_place_aliased.ts")
 tslang_add_test(NAME test-jit-00-temporary-read-in-finally COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00temporary_read_in_finally.ts")
 tslang_add_test(NAME test-jit-00-unowned-local-store COMMAND test-runner -jit "${PROJECT_SOURCE_DIR}/test/tester/tests/00unowned_local_store.ts")
@@ -2002,6 +2004,7 @@ set(TSLANG_CORPUS
     00class_to_interface_null.ts
     00null_interface_to_interface.ts
     00interface_type_tag_in_vtable.ts
+    00nullable_interface_to_interface.ts
     00argument_place_aliased.ts
     00temporary_read_in_finally.ts
     00unowned_local_store.ts
diff --git a/tslang/test/tester/tests/00nullable_interface_to_interface.ts b/tslang/test/tester/tests/00nullable_interface_to_interface.ts
new file mode 100644
index 000000000..92ae0b04b
--- /dev/null
+++ b/tslang/test/tester/tests/00nullable_interface_to_interface.ts
@@ -0,0 +1,84 @@
+// An interface-or-null given to another interface-or-null whose interface it does not extend is the
+// interface-to-interface cast (#666), which builds the target's vtable out of the value's own one. A
+// plain copy kept the source's vtable, and a field read through the target read a method slot as the
+// field's offset. A null value is null still, and its methods throw. Not under -mm=own, which does not
+// take this program's interface values returned from calls yet.
+interface Shape {
+    id: number;
+    area(): number;
+}
+
+interface HasId {
+    id: number;
+}
+
+interface Sized {
+    area(): number;
+    id: number;
+}
+
+class Box {
+    constructor(public w: number, public h: number) {}
+}
+
+class Rect implements Shape {
+    constructor(public id: number, public box: Box) {}
+
+    area(): number {
+        return this.box.w * this.box.h;
+    }
+}
+
+class Square extends Rect {
+    constructor(id: number, side: number, public label: Box) {
+        super(id, new Box(side, side));
+    }
+}
+
+@noinline function mkSquare(id: number, side: number): Shape {
+    return new Square(id, side, new Box(id, id));
+}
+
+@noinline function mkShape(flag: boolean): Shape | null {
+    return flag ? mkSquare(5, 2) : null;
+}
+
+@noinline function mkNull(): HasId | null {
+    return null;
+}
+
+// what a method of the interface does: -2 when it throws
+function call(s: Sized | null): number {
+    try {
+        return s.area();
+    } catch (e) {
+        return -2;
+    }
+}
+
+function main() {
+    // a field first, and no method: a method called through a wrong vtable runs whatever code it lands on
+    const b: Shape | null = mkSquare(7, 3);
+    let n: HasId | null = mkNull();
+    n = b;
+    assert(n.id == 7, "a field read through the other interface");
+
+    // members in another order: the field and the method each moved
+    const s: Sized | null = b;
+    assert(s.id == 7, "a field that moved");
+    assert(call(s) == 9, "a method that moved");
+
+    // a declaration, and a value that came back from a call
+    const m: HasId | null = mkShape(true);
+    assert(m.id == 5, "a returned value seen through the other interface");
+
+    // null stays null, and its methods throw
+    const nullShape: Shape | null = mkShape(false);
+    const nullId: HasId | null = nullShape;
+    assert(nullId === null, "null seen through the other interface");
+    const nullSized: Sized | null = nullShape;
+    assert(nullSized === null, "null seen through an interface with members in another order");
+    assert(call(nullSized) == -2, "its method throws");
+
+    print("done.");
+}