diff --git a/htdocs/core/lib/functions.lib.php b/htdocs/core/lib/functions.lib.php
index 014a979927f..b92c0dc56c7 100644
--- a/htdocs/core/lib/functions.lib.php
+++ b/htdocs/core/lib/functions.lib.php
@@ -10851,12 +10851,16 @@ function verifCond($strToEvaluate, $onlysimplestring = '1')
  * @param	string		$onlysimplestring	'0' (deprecated, do not use it anymore)=Accept all chars,
  *                                          '1' (most common use)=Accept only simple string with char 'a-z0-9\s^$_+-.*>&|=!?():"\',/@';',
  *                                          '2' (used for example for the compute property of extrafields)=Accept also '<[]'
- * @return	void|string						Nothing or return result of eval (even if type can be int, it is safer to assume string and find all potential typing issues as abs(dol_eval(...)).
+ * @return	string							Return result of eval (even if type can be int, it is safer to assume string and find all potential typing issues as abs(dol_eval(...)).
  * @see verifCond(), checkPHPCode() to see sanitizing rules that should be very close.
  * @phan-suppress PhanPluginUnsafeEval
  */
 function dol_eval($s, $returnvalue = 1, $hideerrors = 1, $onlysimplestring = '1')
 {
+	if ($returnvalue != 1) {
+		dol_syslog("Use of dol_eval with parameter returnvalue = 0 is now forbidden. Please fix this", LOG_ERR);
+	}
+
 	if (getDolGlobalString("MAIN_USE_DOL_EVAL_NEW")) {
 		return dol_eval_new($s);
 	} else {