diff --git a/thunderbird.spec b/thunderbird.spec
index 6c75258..aaea2aa 100644
--- a/thunderbird.spec
+++ b/thunderbird.spec
@@ -560,7 +560,7 @@ MOZ_SMP_FLAGS=-j1
 
 export MOZ_MAKE_FLAGS="$MOZ_SMP_FLAGS"
 export STRIP=/bin/true
-export MACH_USE_SYSTEM_PYTHON=1
+export MACH_BUILD_PYTHON_NATIVE_PACKAGE_SOURCE=system
 ./mach build -v
 
 # create debuginfo for crash-stats.mozilla.com