diff --git a/doc/manual-src/en/aria2c.rst b/doc/manual-src/en/aria2c.rst
index 6722e0d2..2ec013fe 100644
--- a/doc/manual-src/en/aria2c.rst
+++ b/doc/manual-src/en/aria2c.rst
@@ -1400,7 +1400,7 @@ Advanced Options
 .. option:: --gid=<GID>
 
   Set GID manually. aria2 identifies each download by the ID called
-  GID. The GID must be hex string of 16 characters, thus [0-9a-zA-Z]
+  GID. The GID must be hex string of 16 characters, thus [0-9a-fA-F]
   are allowed and leading zeros must not be stripped. The GID all 0 is
   reserved and must not be used. The GID must be unique, otherwise
   error is reported and the download is not added.  This option is
diff --git a/src/usage_text.h b/src/usage_text.h
index d73b50d9..ebf67e3d 100644
--- a/src/usage_text.h
+++ b/src/usage_text.h
@@ -1002,7 +1002,7 @@
 #define TEXT_GID                                \
   _(" --gid=GID                    Set GID manually. aria2 identifies each\n" \
     "                              download by the ID called GID. The GID must be\n" \
-    "                              hex string of 16 characters, thus [0-9a-zA-Z]\n" \
+    "                              hex string of 16 characters, thus [0-9a-fA-F]\n" \
     "                              are allowed and leading zeros must not be\n" \
     "                              stripped. The GID all 0 is reserved and must\n" \
     "                              not be used. The GID must be unique, otherwise\n" \