diff --git a/proofmode/tactics.v b/proofmode/tactics.v
index 49e373371c9428544909a353b691b5830fc5199d..dcf66b391b5f1d69ed2c6a81e789f9b470328b0b 100644
--- a/proofmode/tactics.v
+++ b/proofmode/tactics.v
@@ -508,14 +508,15 @@ Tactic Notation "iTimeless" constr(H) :=
Tactic Notation "iVsIntro" :=
eapply tac_vs_intro;
[let P := match goal with |- FromVs ?P _ => P end in
- apply _ || fail "iVsIntro:" P "not a viewshift"|].
+ apply _ || fail "iVsIntro:" P "not a view shift"|].
Tactic Notation "iVsCore" constr(H) :=
eapply tac_vs_elim with _ H _ _ _ _;
[env_cbv; reflexivity || fail "iVs:" H "not found"
|let P := match goal with |- ElimVs ?P _ _ _ => P end in
- let Q := match goal with |- ElimVs _ _ _ ?Q => Q end in
- apply _ || fail "iVs: cannot eliminate" H ":" P "in" Q
+ let Q := match goal with |- ElimVs _ _ ?Q _ => Q end in
+ apply _ || fail "iVs: cannot run" H ":" P "in" Q
+ "because the goal or hypothesis is not a view shift"
|env_cbv; reflexivity|].
(** * Basic destruct tactic *)