diff --git a/theories/vcgen/vcg.v b/theories/vcgen/vcg.v
index e88bc47d936933603f681cdff32873ac3ae7d372..cbea760b8dc4188fe48b1ae92c4eee71c55d528e 100644
--- a/theories/vcgen/vcg.v
+++ b/theories/vcgen/vcg.v
@@ -251,6 +251,8 @@ Section vcg.
            | _ =>
               wand_denv_interp E m (
                 ⌜dval_interp E dv1 = #true⌝ ∧
+                (* FIXME, make sure that computation of vcg is blocked in the
+                continuation. *)
                 U (vcg_continuation E (λ E m dv,
                      vcg E n m (dCSeqBind <> de2 (dCWhileV de1 de2)) R Φ) #())
                 ∨ ⌜dval_interp E dv1 = #false⌝ ∧