diff --git a/spec.bs b/spec.bs
index a567e5a..caab756 100644
--- a/spec.bs
+++ b/spec.bs
@@ -468,7 +468,7 @@ A <dfn>component</dfn> is a [=struct=] with the following [=struct/items=]:
 </div>
 
 <div algorithm>
-  To perform a <dfn export for="URL pattern">match</dfn> given a [=URL pattern=] |urlPattern|, a {{URLPatternInput}} |input|, and an optional string |baseURLString|:
+  To perform a <dfn export for="URL pattern">match</dfn> given a [=URL pattern=] |urlPattern|, a {{URLPatternInput}} or [=/URL=] |input|, and an optional string |baseURLString|:
 
   1. Let |protocol| be the empty string.
   1. Let |username| be the empty string.
@@ -492,13 +492,16 @@ A <dfn>component</dfn> is a [=struct=] with the following [=struct/items=]:
     1. Set |search| to |applyResult|["{{URLPatternInit/search}}"].
     1. Set |hash| to |applyResult|["{{URLPatternInit/hash}}"].
   1. Otherwise:
-    1. Let |baseURL| be null.
-    1. If |baseURLString| was given, then:
-      1. Set |baseURL| to the result of [=URL parser|parsing=] |baseURLString|.
-      1. If |baseURL| is failure, return null.
-      1. [=list/Append=] |baseURLString| to |inputs|.
-    1. Let |url| be the result of [=URL parser|parsing=] |input| given |baseURL|.
-    1. If |url| is failure, return null.
+    1. Let |url| be |input|.
+    1. If |input| is a {{USVString}}:
+      1. Let |baseURL| be null.
+      1. If |baseURLString| was given, then:
+        1. Set |baseURL| to the result of [=URL parser|parsing=] |baseURLString|.
+        1. If |baseURL| is failure, return null.
+        1. [=list/Append=] |baseURLString| to |inputs|.
+      1. Set |url| to the result of [=URL parser|parsing=] |input| given |baseURL|.
+      1. If |url| is failure, return null.
+    1. [=Assert=]: |url| is a [=/URL=].
     1. Set |protocol| to |url|'s [=url/scheme=].
     1. Set |username| to |url|'s [=url/username=].
     1. Set |password| to |url|'s [=url/password=].