diff --git a/aurweb/templates.py b/aurweb/templates.py
index 9439f3a3..1e09bf61 100644
--- a/aurweb/templates.py
+++ b/aurweb/templates.py
@@ -26,6 +26,7 @@ env.filters["tr"] = l10n.tr
 # Utility filters.
 env.filters["dt"] = util.timestamp_to_datetime
 env.filters["as_timezone"] = util.as_timezone
+env.filters["dedupe_qs"] = util.dedupe_qs
 
 # Add captcha filters.
 env.filters["captcha_salt"] = captcha.captcha_salt_filter
diff --git a/aurweb/util.py b/aurweb/util.py
index 1615e00a..0aec6f45 100644
--- a/aurweb/util.py
+++ b/aurweb/util.py
@@ -3,8 +3,9 @@ import random
 import re
 import string
 
+from collections import OrderedDict
 from datetime import datetime
-from urllib.parse import urlparse
+from urllib.parse import quote_plus, urlparse
 from zoneinfo import ZoneInfo
 
 from email_validator import EmailNotValidError, EmailUndeliverableError, validate_email
@@ -106,6 +107,29 @@ def as_timezone(dt: datetime, timezone: str):
     return dt.astimezone(tz=ZoneInfo(timezone))
 
 
+def dedupe_qs(query_string: str, *additions):
+    """ Dedupe keys found in a query string by rewriting it without
+    duplicates found while iterating from the end to the beginning,
+    using an ordered memo to track keys found and persist locations.
+
+    That is, query string 'a=1&b=1&a=2' will be deduped and converted
+    to 'b=1&a=2'.
+
+    :param query_string: An HTTP URL query string.
+    :param *additions: Optional additional fields to add to the query string.
+    :return: Deduped query string, including *additions at the tail.
+    """
+    for addition in list(additions):
+        query_string += f"&{addition}"
+
+    qs = OrderedDict()
+    for item in reversed(query_string.split('&')):
+        key, value = item.split('=')
+        if key not in qs:
+            qs[key] = value
+    return '&'.join([f"{k}={quote_plus(v)}" for k, v in reversed(qs.items())])
+
+
 def jsonify(obj):
     """ Perform a conversion on obj if it's needed. """
     if isinstance(obj, datetime):
diff --git a/test/test_util.py b/test/test_util.py
index d58a8ae2..074de494 100644
--- a/test/test_util.py
+++ b/test/test_util.py
@@ -1,3 +1,4 @@
+from collections import OrderedDict
 from datetime import datetime
 from zoneinfo import ZoneInfo
 
@@ -14,3 +15,18 @@ def test_as_timezone():
     ts = datetime.utcnow().timestamp()
     dt = util.timestamp_to_datetime(ts)
     assert util.as_timezone(dt, "UTC") == dt.astimezone(tz=ZoneInfo("UTC"))
+
+
+def test_dedupe_qs():
+    items = OrderedDict()
+    items["key1"] = "test"
+    items["key2"] = "blah"
+    items["key3"] = 1
+
+    # Construct and test our query string.
+    query_string = '&'.join([f"{k}={v}" for k, v in items.items()])
+    assert query_string == "key1=test&key2=blah&key3=1"
+
+    # Add key1=changed and key2=changed to the query and dedupe it.
+    deduped = util.dedupe_qs(query_string, "key1=changed", "key3=changed")
+    assert deduped == "key2=blah&key1=changed&key3=changed"