diff --git a/android/defaults_test.go b/android/defaults_test.go
index a7542ab..d80f40c 100644
--- a/android/defaults_test.go
+++ b/android/defaults_test.go
@@ -19,7 +19,14 @@
 )
 
 type defaultsTestProperties struct {
-	Foo []string
+	Foo    []string
+	Bar    []string
+	Nested struct {
+		Fizz *bool
+	}
+	Other struct {
+		Buzz *string
+	}
 }
 
 type defaultsTestModule struct {
@@ -130,3 +137,167 @@
 	// TODO: missing transitive defaults is currently not handled
 	_ = missingTransitiveDefaults
 }
+
+func TestProtectedProperties_ProtectedPropertyNotSet(t *testing.T) {
+	bp := `
+		defaults {
+			name: "transitive",
+			protected_properties: ["foo"],
+		}
+	`
+
+	GroupFixturePreparers(
+		prepareForDefaultsTest,
+		FixtureWithRootAndroidBp(bp),
+	).ExtendWithErrorHandler(FixtureExpectsAtLeastOneErrorMatchingPattern(
+		"module \"transitive\": foo: is not set; protected properties must be explicitly set")).
+		RunTest(t)
+}
+
+func TestProtectedProperties_ProtectedPropertyNotLeaf(t *testing.T) {
+	bp := `
+		defaults {
+			name: "transitive",
+			protected_properties: ["nested"],
+			nested: {
+				fizz: true,
+			},
+		}
+	`
+
+	GroupFixturePreparers(
+		prepareForDefaultsTest,
+		FixtureWithRootAndroidBp(bp),
+	).ExtendWithErrorHandler(FixtureExpectsAtLeastOneErrorMatchingPattern(
+		`\Qmodule "transitive": nested: property is not supported by this module type "defaults"\E`)).
+		RunTest(t)
+}
+
+// TestProtectedProperties_ApplyDefaults makes sure that the protected_properties property has
+// defaults applied.
+func TestProtectedProperties_HasDefaultsApplied(t *testing.T) {
+
+	bp := `
+		defaults {
+			name: "transitive",
+			protected_properties: ["foo"],
+			foo: ["transitive"],
+		}
+
+		defaults {
+			name: "defaults",
+			defaults: ["transitive"],
+			protected_properties: ["bar"],
+			bar: ["defaults"],
+		}
+	`
+
+	result := GroupFixturePreparers(
+		prepareForDefaultsTest,
+		FixtureWithRootAndroidBp(bp),
+	).RunTest(t)
+
+	defaults := result.Module("defaults", "").(DefaultsModule)
+	AssertDeepEquals(t, "defaults protected properties", []string{"foo", "bar"}, defaults.protectedProperties())
+}
+
+// TestProtectedProperties_ProtectAllProperties makes sure that protected_properties: ["*"] protects
+// all properties.
+func TestProtectedProperties_ProtectAllProperties(t *testing.T) {
+
+	bp := `
+		defaults {
+			name: "transitive",
+			protected_properties: ["other.buzz"],
+			other: {
+				buzz: "transitive",
+			},
+		}
+
+		defaults {
+			name: "defaults",
+			defaults: ["transitive"],
+			visibility: ["//visibility:private"],
+			protected_properties: ["*"],
+			foo: ["other"],
+			bar: ["defaults"],
+			nested: {
+				fizz: true,
+			}
+		}
+	`
+
+	result := GroupFixturePreparers(
+		prepareForDefaultsTest,
+		FixtureWithRootAndroidBp(bp),
+	).RunTest(t)
+
+	defaults := result.Module("defaults", "").(DefaultsModule)
+	AssertDeepEquals(t, "defaults protected properties", []string{"other.buzz", "bar", "foo", "nested.fizz"},
+		defaults.protectedProperties())
+}
+
+func TestProtectedProperties_DetectedOverride(t *testing.T) {
+	bp := `
+		defaults {
+			name: "defaults",
+			protected_properties: ["foo", "nested.fizz"],
+			foo: ["defaults"],
+			nested: {
+				fizz: true,
+			},
+		}
+
+		test {
+			name: "foo",
+			defaults: ["defaults"],
+			foo: ["module"],
+			nested: {
+				fizz: false,
+			},
+		}
+	`
+
+	GroupFixturePreparers(
+		prepareForDefaultsTest,
+		FixtureWithRootAndroidBp(bp),
+	).ExtendWithErrorHandler(FixtureExpectsAllErrorsToMatchAPattern(
+		[]string{
+			`\Qmodule "foo": attempts to append ["module"] to protected property "foo"'s value of ["defaults"] defined in module "defaults"\E`,
+			`\Qmodule "foo": attempts to override protected property "nested.fizz" defined in module "defaults" with a different value (override true with false) so removing the property may necessitate other changes.\E`,
+		})).RunTest(t)
+}
+
+func TestProtectedProperties_DefaultsConflict(t *testing.T) {
+	bp := `
+		defaults {
+			name: "defaults1",
+			protected_properties: ["other.buzz"],
+			other: {
+				buzz: "value",
+			},
+		}
+
+		defaults {
+			name: "defaults2",
+			protected_properties: ["other.buzz"],
+			other: {
+				buzz: "another",
+			},
+		}
+
+		test {
+			name: "foo",
+			defaults: ["defaults1", "defaults2"],
+		}
+	`
+
+	GroupFixturePreparers(
+		prepareForDefaultsTest,
+		FixtureWithRootAndroidBp(bp),
+	).ExtendWithErrorHandler(FixtureExpectsAtLeastOneErrorMatchingPattern(
+		`\Qmodule "foo": has conflicting default values for protected property "other.buzz":
+    defaults module "defaults1" provides value "value"
+    defaults module "defaults2" provides value "another"\E`,
+	)).RunTest(t)
+}