diff --git a/README.md b/README.md
index e504914..9b2467a 100644
--- a/README.md
+++ b/README.md
@@ -315,7 +315,7 @@ String
 <bool> = <str>.startswith(<sub_str>)         # Pass tuple of strings for multiple options.
 <bool> = <str>.endswith(<sub_str>)           # Pass tuple of strings for multiple options.
 <int>  = <str>.find(<sub_str>)               # Returns start index of first match or -1.
-<int>  = <str>.index(<sub_str>)              # Same but raises ValueError.
+<int>  = <str>.index(<sub_str>)              # Same but raises ValueError if missing.
 ```
 
 ```python
diff --git a/index.html b/index.html
index 2f7cea5..8313938 100644
--- a/index.html
+++ b/index.html
@@ -429,7 +429,7 @@ to_exclusive   = &lt;range&gt;.stop
 &lt;bool&gt; = &lt;str&gt;.startswith(&lt;sub_str&gt;)         <span class="hljs-comment"># Pass tuple of strings for multiple options.</span>
 &lt;bool&gt; = &lt;str&gt;.endswith(&lt;sub_str&gt;)           <span class="hljs-comment"># Pass tuple of strings for multiple options.</span>
 &lt;int&gt;  = &lt;str&gt;.find(&lt;sub_str&gt;)               <span class="hljs-comment"># Returns start index of first match or -1.</span>
-&lt;int&gt;  = &lt;str&gt;.index(&lt;sub_str&gt;)              <span class="hljs-comment"># Same but raises ValueError.</span>
+&lt;int&gt;  = &lt;str&gt;.index(&lt;sub_str&gt;)              <span class="hljs-comment"># Same but raises ValueError if missing.</span>
 </code></pre>
 <pre><code class="python language-python hljs">&lt;str&gt;  = &lt;str&gt;.replace(old, new [, count])   <span class="hljs-comment"># Replaces 'old' with 'new' at most 'count' times.</span>
 &lt;bool&gt; = &lt;str&gt;.isnumeric()                   <span class="hljs-comment"># True if str contains only numeric characters.</span>