diff --git a/index.bs b/index.bs
index 6f86e33..fd3c0bc 100644
--- a/index.bs
+++ b/index.bs
@@ -258,7 +258,7 @@ To <dfn for="model context">unregister a tool</dfn> given a {{ModelContext}} |mo
 1. Let |tool map| be |modelContext|'s [=ModelContext/internal context=]'s [=model context/tool
    map=].
 
-1. [=Assert=] |tool map|[|tool name|] [=map/exists=].
+1. If |tool map|[|tool name|] does not [=map/exist=], then return.
 
 1. Let |exposed origins| be |tool map|[|tool name|]'s [=tool definition/exposed origins=].
 
@@ -395,16 +395,20 @@ The <dfn method for=ModelContext>registerTool(<var>tool</var>, <var>options</var
 1. Let |untrusted content hint| be true if |tool|'s {{ModelContextTool/annotations}} [=map/exists=] and
    its {{ToolAnnotations/untrustedContentHint}} is true. Otherwise, let it be false.
 
+1. Let |promise| be [=a new promise=] created in [=this=]'s [=relevant realm=].
+
 1. Let |signal| be |options|'s {{ModelContextRegisterToolOptions/signal}}.
 
 1. If |signal| [=map/exists=], then:
 
-   1. If |signal| is [=AbortSignal/aborted=], then optionally [=report a warning to the console=]
-      indicating that the tool was not registered because the {{AbortSignal}} was already
-      [=AbortSignal/aborted=], and return.
+   1. If |signal| is [=AbortSignal/aborted=], then return [=a promise rejected with=]
+      |signal|'s [=AbortSignal/abort reason=].
+
+   1. [=AbortSignal/add|Add the following abort steps=] to |signal|:
 
-   1. [=AbortSignal/add|Add an abort algorithm=] to |signal| that [=model context/unregisters a
-      tool=] given [=this=] and |tool name|.
+        1. [=model context/Unregister a tool=] given [=this=] and |tool name|.
+
+        1. [=Reject=] |promise| with |signal|'s [=AbortSignal/abort reason=].
 
 1. Let |exposed origins| be an empty [=list=] of [=origins=].
 
@@ -448,8 +452,6 @@ The <dfn method for=ModelContext>registerTool(<var>tool</var>, <var>options</var
 
 1. Set [=this=]'s [=ModelContext/internal context=][|tool name|] to |tool definition|.
 
-1. Let |promise| be [=a new promise=] created in [=this=]'s [=relevant realm=].
-
 1. Run the following steps [=in parallel=]:
 
   1. [=Notify documents of a tool change=] given |tool owner| and |exposed origins|.