diff --git a/Documentation/git-interpret-trailers.adoc b/Documentation/git-interpret-trailers.adoc
index 109059f11e..fb503cbe95 100644
--- a/Documentation/git-interpret-trailers.adoc
+++ b/Documentation/git-interpret-trailers.adoc
@@ -18,7 +18,8 @@ Add or parse trailer metadata at the end of the otherwise
 free-form part of a commit message, or any other kind of text.
 
 A _trailer_ in its simplest form is a key-value pair with a colon as a
-separator. A _trailer block_ consists of one or more trailers. The
+separator. The _key_ consists of ASCII alphanumeric characters and
+hyphens (`-`). A _trailer block_ consists of one or more trailers. The
 trailer block needs to be preceded by a blank line, where a _blank line_
 is either an empty or a whitespace-only line. For example, in the
 following commit message