diff --git a/spec.bs b/spec.bs
index 8c886bc..c0d23c7 100644
--- a/spec.bs
+++ b/spec.bs
@@ -199,7 +199,8 @@ The <dfn attribute for=Subscriber><code>signal</code></dfn> getter steps are to
     1. If [=this=]'s [=relevant global object=] is a {{Window}} object, and its [=associated
        Document=] is not [=Document/fully active=], then return.
 
-    1. Run [=this=]'s [=Subscriber/next algorithm=] algorithm given |value|.
+    1. If [=this=]'s [=Subscriber/next algorithm=] is not null, then run [=this=]'s
+       [=Subscriber/next algorithm=] given |value|.
 
        [=Assert=]: No <a spec=webidl lt="an exception was thrown">exception was thrown</a>.
 </div>
@@ -214,10 +215,12 @@ The <dfn attribute for=Subscriber><code>signal</code></dfn> getter steps are to
 
     1. [=close a subscription|Close=] [=this=].
 
-    1. Run |error algorithm| given |error|.
+    1. If |error algorithm| is not null, then run |error algorithm| given |error|.
 
        [=Assert=]: No <a spec=webidl lt="an exception was thrown">exception was thrown</a>.
 
+    1. Otherwise (i.e., when |error algorithm| is null), [=report the exception=] |error|.
+
     1. [=AbortController/Signal abort=] [=this=]'s [=Subscriber/complete or error controller=].
 </div>
 
@@ -231,7 +234,7 @@ The <dfn attribute for=Subscriber><code>signal</code></dfn> getter steps are to
 
     1. [=close a subscription|Close=] [=this=].
 
-    1. Run |complete algorithm|.
+    1. If |complete algorithm| is not null, then run |complete algorithm|.
 
        [=Assert=]: No <a spec=webidl lt="an exception was thrown">exception was thrown</a>.