diff --git a/tools/fuchsia/dart/gen_dart_package_config.py b/tools/fuchsia/dart/gen_dart_package_config.py
index 71a8bb3666c91..d46ba0f8dafde 100755
--- a/tools/fuchsia/dart/gen_dart_package_config.py
+++ b/tools/fuchsia/dart/gen_dart_package_config.py
@@ -15,7 +15,7 @@
 import sys
 
 THIS_DIR = os.path.abspath(os.path.dirname(__file__))
-sys.path += [os.path.join(THIS_DIR, '..', '..', '..', 'third_party', 'pyyaml', 'lib')]
+sys.path.insert(0, os.path.join(THIS_DIR, '..', '..', '..', 'third_party', 'pyyaml', 'lib'))
 import yaml
 
 DEFAULT_LANGUAGE_VERSION = '2.8'
diff --git a/tools/pub_get_offline.py b/tools/pub_get_offline.py
index 56e1d8d0d89a2..2195a676a7db6 100644
--- a/tools/pub_get_offline.py
+++ b/tools/pub_get_offline.py
@@ -15,7 +15,7 @@
 import sys
 
 THIS_DIR = os.path.abspath(os.path.dirname(__file__))
-sys.path += [os.path.join(THIS_DIR, '..', 'third_party', 'pyyaml', 'lib')]
+sys.path.insert(0, os.path.join(THIS_DIR, '..', 'third_party', 'pyyaml', 'lib'))
 import yaml  # pylint: disable=import-error, wrong-import-position
 
 SRC_ROOT = os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))