diff --git a/theories/bi/derived_laws.v b/theories/bi/derived_laws.v
index ae10b064312182e967f118f2ed3a7c24d4b20c52..f43bf74ed102c9878e7045befbfab305242dea0c 100644
--- a/theories/bi/derived_laws.v
+++ b/theories/bi/derived_laws.v
@@ -1083,6 +1083,13 @@ Qed.
Lemma impl_wand_plainly_2 P Q : (bi_plainly P -∗ Q) ⊢ (bi_plainly P → Q).
Proof. apply impl_intro_l. by rewrite plainly_and_sep_l_1 wand_elim_r. Qed.
+Lemma valid_plainly P : bi_valid (bi_plainly P) ↔ bi_valid P.
+Proof.
+ rewrite /bi_valid. split; intros HP.
+ - by rewrite -(idemp bi_and emp%I) {2}HP plainly_and_emp_elim.
+ - by rewrite (plainly_emp_intro emp%I) HP.
+Qed.
+
Section plainly_affinely_bi.
Context `{BiAffine PROP}.