diff --git a/src/autolink_references/main.py b/src/autolink_references/main.py
index 4bf5cb0..e464f80 100755
--- a/src/autolink_references/main.py
+++ b/src/autolink_references/main.py
@@ -7,11 +7,11 @@ def replace_autolink_references(markdown, ref_prefix, target_url):
     if "<num>" not in ref_prefix:
         ref_prefix = ref_prefix + "<num>"
     find_regex = re.compile(
-        r"(?<![#\[/])" + ref_prefix.replace(r"<num>", r"(?P<num>[-\w]+)")
+        r"(?<![#\[/])" + ref_prefix.replace(r"<num>", r"(?P<num>[-\w]+)"), re.IGNORECASE
     )
     linked_ref = rf"[{ref_prefix}](" + target_url + r")"
     replace_text = linked_ref.replace(r"<num>", r"\g<num>")
-    markdown = re.sub(find_regex, replace_text, markdown, re.IGNORECASE)
+    markdown = re.sub(find_regex, replace_text, markdown)
     return markdown