diff --git a/emark/message.py b/emark/message.py
index b08f7a6..fac24b6 100644
--- a/emark/message.py
+++ b/emark/message.py
@@ -131,7 +131,7 @@ def inject_utm_params(self, md, **utm):
         for url in INLINE_LINK_RE.findall(md):
             try:
                 url_parts = parse.urlparse(url)
-                if url_parts.scheme not in [
+                if url_parts.scheme.lower() not in [
                     "http",
                     "https",
                     "",
@@ -143,7 +143,7 @@ def inject_utm_params(self, md, **utm):
         for url in INLINE_HTML_LINK_RE.findall(md):
             try:
                 url_parts = parse.urlparse(url)
-                if url_parts.scheme not in [
+                if url_parts.scheme.lower() not in [
                     "http",
                     "https",
                     "",
diff --git a/tests/test_message.py b/tests/test_message.py
index 6853250..1d4a308 100644
--- a/tests/test_message.py
+++ b/tests/test_message.py
@@ -280,6 +280,10 @@ def test_inject_utm_params(self):
             "A link without www <example.com?utm_source=website&utm_medium=email&utm_campaign=MARKDOWN_EMAIL_TEST_WITH_SUBJECT>"
             in email_message.body
         )
+        assert (
+            "ALL CAPS LINK <http://WWW.EXAMPLE.COM?utm_source=website&utm_medium=email&utm_campaign=MARKDOWN_EMAIL_TEST_WITH_SUBJECT>"
+            in email_message.body
+        )
         assert (
             "localhost:8000 <http://localhost:8000?utm_source=website&utm_medium=email&utm_campaign=MARKDOWN_EMAIL_TEST_WITH_SUBJECT>"
             in email_message.body
diff --git a/tests/testapp/templates/template.md b/tests/testapp/templates/template.md
index c597367..4914d0a 100644
--- a/tests/testapp/templates/template.md
+++ b/tests/testapp/templates/template.md
@@ -13,6 +13,7 @@ Vanilla lollipop biscuit cake marzipan jelly.
 [A link with parameter](https://www.example.com/?foo=bar)
 [A link without a scheme](www.example.com)
 [A link without www](example.com)
+[ALL CAPS LINK](HTTP://WWW.EXAMPLE.COM)
 [localhost:8000](http://localhost:8000)
 [555-2368](tel:5552368)