diff --git a/src/optionstr.c b/src/optionstr.c
index fa7084c..06958aa 100644
--- a/src/optionstr.c
+++ b/src/optionstr.c
@@ -1174,6 +1174,10 @@
 		*curbuf->b_p_cm == NUL ? p_cm : curbuf->b_p_cm);
 	changed_internal();
     }
+# ifdef FEAT_SODIUM
+    if (crypt_method_is_sodium(crypt_get_method_nr(curbuf)))
+       crypt_sodium_lock_key(args->os_newval.string);
+# endif
 
     return NULL;
 }