diff --git a/httpx/_client.py b/httpx/_client.py
index dad4a42aab..0a2e525a2f 100644
--- a/httpx/_client.py
+++ b/httpx/_client.py
@@ -208,7 +208,7 @@ def _merge_url(self, url: URLTypes) -> URL:
         Merge a URL argument together with any 'base_url' on the client,
         to create the URL used for the outgoing request.
         """
-        return self.base_url.join(relative_url=url)
+        return self.base_url.join(url)
 
     def _merge_cookies(
         self, cookies: CookieTypes = None
diff --git a/httpx/_models.py b/httpx/_models.py
index 9c5aa1773a..41c7a274e6 100644
--- a/httpx/_models.py
+++ b/httpx/_models.py
@@ -183,17 +183,17 @@ def copy_with(self, **kwargs: typing.Any) -> "URL":
 
         return URL(self._uri_reference.copy_with(**kwargs).unsplit(),)
 
-    def join(self, relative_url: URLTypes) -> "URL":
+    def join(self, url: URLTypes) -> "URL":
         """
         Return an absolute URL, using given this URL as the base.
         """
         if self.is_relative_url:
-            return URL(relative_url)
+            return URL(url)
 
         # We drop any fragment portion, because RFC 3986 strictly
         # treats URLs with a fragment portion as not being absolute URLs.
         base_uri = self._uri_reference.copy_with(fragment=None)
-        relative_url = URL(relative_url)
+        relative_url = URL(url)
         return URL(relative_url._uri_reference.resolve_with(base_uri).unsplit())
 
     def __hash__(self) -> int: