diff --git a/proselint/checks/mau_a_vs_an.py b/proselint/checks/mau_a_vs_an.py
index b34c54e11..48120554e 100644
--- a/proselint/checks/mau_a_vs_an.py
+++ b/proselint/checks/mau_a_vs_an.py
@@ -48,7 +48,7 @@ def starts_with_vowel_sound(word):
             return None
 
     errors = []
-    regex = re.compile("(^|\s+)(A|a|An|an)\s(\S*)\W")
+    regex = re.compile("(?:^|\W)(an?)\s+(\w+)", re.IGNORECASE)
 
     # Find all occurences of the regex in the text.
     for m in regex.finditer(text):