diff --git a/src/vars.c b/src/vars.c
index e328999..251ffe1 100644
--- a/src/vars.c
+++ b/src/vars.c
@@ -585,9 +585,13 @@
 }
 
 
-/* this function fills a sample with the
- * variable content. Returns 1 if the sample
- * is filled, otherwise it returns 0.
+/* This function fills a sample with the variable content.
+ *
+ * Keep in mind that a sample content is duplicated by using smp_dup()
+ * and it therefore uses a pre-allocated trash chunk as returned by
+ * get_trash_chunk().
+ *
+ * Returns 1 if the sample is filled, otherwise it returns 0.
  */
 int vars_get_by_name(const char *name, size_t len, struct sample *smp)
 {
@@ -606,19 +610,29 @@
 		return 0;
 
 	/* Get the variable entry. */
+	HA_RWLOCK_RDLOCK(VARS_LOCK, &vars->rwlock);
 	var = var_get(vars, name);
-	if (!var)
+	if (!var) {
+		HA_RWLOCK_RDUNLOCK(VARS_LOCK, &vars->rwlock);
 		return 0;
+	}
 
 	/* Copy sample. */
 	smp->data = var->data;
-	smp->flags = SMP_F_CONST;
+	smp_dup(smp);
+
+	HA_RWLOCK_RDUNLOCK(VARS_LOCK, &vars->rwlock);
 	return 1;
 }
 
-/* this function fills a sample with the
- * content of the variable described by <var_desc>. Returns 1
- * if the sample is filled, otherwise it returns 0.
+/* This function fills a sample with the content of the variable described
+ * by <var_desc>.
+ *
+ * Keep in mind that a sample content is duplicated by using smp_dup()
+ * and it therefore uses a pre-allocated trash chunk as returned by
+ * get_trash_chunk().
+ *
+ * Returns 1 if the sample is filled, otherwise it returns 0.
  */
 int vars_get_by_desc(const struct var_desc *var_desc, struct sample *smp)
 {
@@ -633,13 +647,18 @@
 		return 0;
 
 	/* Get the variable entry. */
+	HA_RWLOCK_RDLOCK(VARS_LOCK, &vars->rwlock);
 	var = var_get(vars, var_desc->name);
-	if (!var)
+	if (!var) {
+		HA_RWLOCK_RDUNLOCK(VARS_LOCK, &vars->rwlock);
 		return 0;
+	}
 
 	/* Copy sample. */
 	smp->data = var->data;
-	smp->flags = SMP_F_CONST;
+	smp_dup(smp);
+
+	HA_RWLOCK_RDUNLOCK(VARS_LOCK, &vars->rwlock);
 	return 1;
 }