diff --git a/grow/preprocessors/file_watchers.py b/grow/preprocessors/file_watchers.py
index e81731f50..0c6cdfb09 100644
--- a/grow/preprocessors/file_watchers.py
+++ b/grow/preprocessors/file_watchers.py
@@ -8,6 +8,7 @@
 
 
 IGNORED_PATTERNS = [
+    '*{sep}extensions{sep}*'.format(sep=os.sep),
     '*{sep}node_modules{sep}*'.format(sep=os.sep),
     '*{sep}build{sep}*'.format(sep=os.sep),
 ]