diff --git a/docs/libcurl/opts/CURLSHOPT_SHARE.md b/docs/libcurl/opts/CURLSHOPT_SHARE.md
index d4e3fc4dfb..4171430a79 100644
--- a/docs/libcurl/opts/CURLSHOPT_SHARE.md
+++ b/docs/libcurl/opts/CURLSHOPT_SHARE.md
@@ -35,6 +35,9 @@ CURLSHOPT_SHARE(3) multiple times with different data arguments to have
 the share object share multiple types of data. Unset a type again by setting
 CURLSHOPT_UNSHARE(3).
 
+If any of the data is to be shared in multiple threads then mutex callbacks
+must be set as well. See CURLSHOPT_LOCKFUNC(3) and CURLSHOPT_UNLOCKFUNC(3).
+
 ## CURL_LOCK_DATA_COOKIE
 
 Cookie data is shared across the easy handles using this shared object. Note