diff --git a/sdk/sdk.go b/sdk/sdk.go
index ac6fce9..321d5ab 100644
--- a/sdk/sdk.go
+++ b/sdk/sdk.go
@@ -44,6 +44,9 @@
 	properties sdkProperties
 
 	snapshotFile android.OptionalPath
+
+	// The builder, preserved for testing.
+	builderForTests *snapshotBuilder
 }
 
 type sdkProperties struct {