diff --git a/build/build_unbundled_mainline_module.sh b/build/build_unbundled_mainline_module.sh
index 6c77592..3c7d78b 100755
--- a/build/build_unbundled_mainline_module.sh
+++ b/build/build_unbundled_mainline_module.sh
@@ -118,10 +118,8 @@ function init() {
 
   # This script cannot handle compressed apexes
   declare -grx OVERRIDE_PRODUCT_COMPRESSED_APEX=false
-
-  # UNBUNDLED_BUILD_SDKS_FROM_SOURCE defaults to false, which is necessary to
-  # use prebuilt SDKs on thin branches that may not have the sources (e.g.
-  # frameworks/base).
+  # Unset to build using PreBuilt SDK.
+  declare -grx UNBUNDLED_BUILD_SDKS_FROM_SOURCE=true
 }
 
 function main() {