diff --git a/android/mutator.go b/android/mutator.go
index 9e99bee..3d24c1e 100644
--- a/android/mutator.go
+++ b/android/mutator.go
@@ -202,7 +202,7 @@
 	RegisterPrebuiltsPostDepsMutators,
 	RegisterVisibilityRuleEnforcer,
 	RegisterLicensesDependencyChecker,
-	RegisterNeverallowMutator,
+	registerNeverallowMutator,
 	RegisterOverridePostDepsMutators,
 }
 
diff --git a/android/neverallow.go b/android/neverallow.go
index 7455e6a..a385bbc 100644
--- a/android/neverallow.go
+++ b/android/neverallow.go
@@ -42,7 +42,7 @@
 //     counts as a match
 // - it has none of the "Without" properties matched (same rules as above)
 
-func RegisterNeverallowMutator(ctx RegisterMutatorsContext) {
+func registerNeverallowMutator(ctx RegisterMutatorsContext) {
 	ctx.BottomUp("neverallow", neverallowMutator).Parallel()
 }
 
@@ -661,6 +661,22 @@
 // Overrides the default neverallow rules for the supplied config.
 //
 // For testing only.
-func SetTestNeverallowRules(config Config, testRules []Rule) {
+func setTestNeverallowRules(config Config, testRules []Rule) {
 	config.Once(neverallowRulesKey, func() interface{} { return testRules })
 }
+
+// Prepares for a test by setting neverallow rules and enabling the mutator.
+//
+// If the supplied rules are nil then the default rules are used.
+func PrepareForTestWithNeverallowRules(testRules []Rule) FixturePreparer {
+	return GroupFixturePreparers(
+		FixtureModifyConfig(func(config Config) {
+			if testRules != nil {
+				setTestNeverallowRules(config, testRules)
+			}
+		}),
+		FixtureRegisterWithContext(func(ctx RegistrationContext) {
+			ctx.PostDepsMutators(registerNeverallowMutator)
+		}),
+	)
+}
diff --git a/android/neverallow_test.go b/android/neverallow_test.go
index de0197a..268346a 100644
--- a/android/neverallow_test.go
+++ b/android/neverallow_test.go
@@ -292,7 +292,6 @@
 		ctx.RegisterModuleType("java_library_host", newMockJavaLibraryModule)
 		ctx.RegisterModuleType("java_device_for_host", newMockJavaLibraryModule)
 		ctx.RegisterModuleType("makefile_goal", newMockMakefileGoalModule)
-		ctx.PostDepsMutators(RegisterNeverallowMutator)
 	}),
 )
 
@@ -301,12 +300,7 @@
 		t.Run(test.name, func(t *testing.T) {
 			GroupFixturePreparers(
 				prepareForNeverAllowTest,
-				FixtureModifyConfig(func(config Config) {
-					// If the test has its own rules then use them instead of the default ones.
-					if test.rules != nil {
-						SetTestNeverallowRules(config, test.rules)
-					}
-				}),
+				PrepareForTestWithNeverallowRules(test.rules),
 				test.fs.AddToFixture(),
 			).
 				ExtendWithErrorHandler(FixtureExpectsAllErrorsToMatchAPattern(test.expectedErrors)).