diff --git a/android/defaults.go b/android/defaults.go
index 31d6014..e0e6e5c 100644
--- a/android/defaults.go
+++ b/android/defaults.go
@@ -17,6 +17,7 @@
 import (
 	"reflect"
 
+	"android/soong/ui/metrics/bp2build_metrics_proto"
 	"github.com/google/blueprint"
 	"github.com/google/blueprint/proptools"
 )
@@ -179,7 +180,10 @@
 
 // ConvertWithBp2build to fulfill Bazelable interface; however, at this time defaults module are
 // *NOT* converted with bp2build
-func (defaultable *DefaultsModuleBase) ConvertWithBp2build(ctx TopDownMutatorContext) {}
+func (defaultable *DefaultsModuleBase) ConvertWithBp2build(ctx TopDownMutatorContext) {
+	// Defaults types are never convertible.
+	ctx.MarkBp2buildUnconvertible(bp2build_metrics_proto.UnconvertedReasonType_TYPE_UNSUPPORTED, "")
+}
 
 func InitDefaultsModule(module DefaultsModule) {
 	commonProperties := &commonProperties{}