diff --git a/b2g/confvars.sh b/b2g/confvars.sh
index cc1a7c1f86e..d6830bc5ccf 100644
--- a/b2g/confvars.sh
+++ b/b2g/confvars.sh
@@ -66,3 +66,6 @@ MOZ_JSDOWNLOADS=1
 MOZ_SERVICES_FXACCOUNTS=1
 
 MOZ_BUNDLED_FONTS=1
+
+# Enable exact rooting on b2g.
+JSGC_USE_EXACT_ROOTING=1