diff --git a/doc/go_spec.html b/doc/go_spec.html
index 0f6475eac5a..06dcf3918ef 100644
--- a/doc/go_spec.html
+++ b/doc/go_spec.html
@@ -89,6 +89,9 @@ will use the term <i>character</i> to refer to a Unicode code point.
 Each code point is distinct; for instance, upper and lower case letters
 are different characters.
 </p>
+<p>
+Source code must not contain the NUL character (U+0000).
+</p>
 
 <h3 id="Characters">Characters</h3>