diff --git a/library/Init/Lean/AbstractMetavarContext.lean b/library/Init/Lean/AbstractMetavarContext.lean
index e7aa62aae8..a3566aaec6 100644
--- a/library/Init/Lean/AbstractMetavarContext.lean
+++ b/library/Init/Lean/AbstractMetavarContext.lean
@@ -207,7 +207,7 @@ partial def main [AbstractMetavarContext σ] : Expr → M σ Expr
 
 end InstantiateExprMVars
 
-def instantiateExprMVars [AbstractMetavarContext σ] (e : Expr) : State σ Expr :=
+def instantiateMVars [AbstractMetavarContext σ] (e : Expr) : State σ Expr :=
 if !e.hasMVar then pure e
 else
   adaptState'
diff --git a/library/Init/Lean/LocalContext.lean b/library/Init/Lean/LocalContext.lean
index b54e926e90..61e0e18175 100644
--- a/library/Init/Lean/LocalContext.lean
+++ b/library/Init/Lean/LocalContext.lean
@@ -249,7 +249,7 @@ xs.size.foldRev (fun i b =>
     let ty  := ty.abstractRange i xs;
     let val := val.abstractRange i xs;
     Expr.letE n ty val b
-  | none => b) b
+  | none => panic! "unknown free variable") b
 
 def mkLambda (lctx : LocalContext) (xs : Array Expr) (b : Expr) : Expr :=
 mkBinding true lctx xs b
diff --git a/library/Init/Lean/MetavarContext.lean b/library/Init/Lean/MetavarContext.lean
index 4fbdb7613f..9098ca55de 100644
--- a/library/Init/Lean/MetavarContext.lean
+++ b/library/Init/Lean/MetavarContext.lean
@@ -110,8 +110,8 @@ AbstractMetavarContext.hasAssignedMVar m e
 @[inline] def instantiateLevelMVars (m : MetavarContext) (lvl : Level) : Level × MetavarContext :=
 AbstractMetavarContext.instantiateLevelMVars lvl m
 
-@[inline] def instantiateExprMVars (m : MetavarContext) (e : Expr) : Expr × MetavarContext :=
-AbstractMetavarContext.instantiateExprMVars e m
+@[inline] def instantiateMVars (m : MetavarContext) (e : Expr) : Expr × MetavarContext :=
+AbstractMetavarContext.instantiateMVars e m
 
 end MetavarContext
 end Lean
diff --git a/tests/lean/run/mvar1.lean b/tests/lean/run/mvar1.lean
new file mode 100644
index 0000000000..9af083b0cd
--- /dev/null
+++ b/tests/lean/run/mvar1.lean
@@ -0,0 +1,96 @@
+import Init.Lean.MetavarContext
+open Lean
+
+def check (b : Bool) : IO Unit :=
+unless b (throw "error")
+
+def f := Expr.const `f []
+def g := Expr.const `g []
+def a := Expr.const `a []
+def b := Expr.const `b []
+def c := Expr.const `c []
+
+def b0 := Expr.bvar 0
+def b1 := Expr.bvar 1
+def b2 := Expr.bvar 2
+
+def u := Level.param `u
+
+def typeE := Expr.sort Level.one
+def natE  := Expr.const `Nat []
+def boolE := Expr.const `Bool []
+def vecE  := Expr.const `Vec [Level.zero]
+
+def α := Expr.fvar `α
+def x := Expr.fvar `x
+def y := Expr.fvar `y
+def z := Expr.fvar `z
+def w := Expr.fvar `w
+
+def m1 := Expr.mvar `m1
+def m2 := Expr.mvar `m2
+def m3 := Expr.mvar `m3
+def m4 := Expr.mvar `m4
+def m5 := Expr.mvar `m5
+def m6 := Expr.mvar `m6
+
+def bi := BinderInfo.default
+def arrow (d b : Expr) := Expr.forallE `_ bi d b
+
+def lctx1 : LocalContext := {}
+def lctx2 := lctx1.mkLocalDecl `α `α typeE
+def lctx3 := lctx2.mkLocalDecl `x `x natE
+def lctx4 := lctx3.mkLocalDecl `y `y α
+def lctx5 := lctx4.mkLocalDecl `z `z (mkApp vecE #[x])
+def lctx6 := lctx5.mkLocalDecl `w `w (arrow natE (mkApp m6 #[α, x, y]))
+
+def t1 := lctx5.mkLambda #[α, x, y] $ mkApp f #[α, mkApp g #[x, y], lctx5.mkLambda #[z] (Expr.app f z)]
+#eval check (!t1.hasFVar)
+#eval t1
+
+def mctx1 : MetavarContext := {}
+def mctx2  := mctx1.mkDecl `m1 `m1 lctx3 natE
+def mctx3  := mctx2.mkDecl `m2 `m2 lctx4 α
+def mctx4  := mctx3.mkDecl `m3 `m3 lctx4 natE
+def mctx5  := mctx4.mkDecl `m4 `m4 lctx1 (arrow typeE (arrow natE (arrow α natE)))
+def mctx6  := mctx5.mkDecl `m5 `m5 lctx5 typeE
+def mctx7  := mctx5.mkDecl `m6 `m6 lctx5 (arrow typeE (arrow natE (arrow α natE)))
+def mctx8  := mctx7.assignDelayed `m4 lctx4 #[α, x, y] m3
+def mctx9  := mctx8.assignExpr `m3 (mkApp g #[x, y])
+def mctx10 := mctx9.assignExpr `m1 a
+
+def t2 := lctx5.mkLambda #[α, x, y] $ mkApp f #[mkApp m4 #[α, x, y], x]
+
+#eval check (!t2.hasFVar)
+#eval t2
+#eval (mctx6.instantiateMVars t2).1
+#eval check (!(mctx9.instantiateMVars t2).1.hasMVar)
+#eval check (!(mctx9.instantiateMVars t2).1.hasFVar)
+#eval (mctx9.instantiateMVars t2).1
+
+-- t3 is ill-formed since m3's localcontext contains ‵α`, `x` and `y`
+def t3 := lctx5.mkLambda #[α, x, y] $ mkApp f #[m3, x]
+#eval check (mctx10.instantiateMVars t3).1.hasFVar
+#eval (mctx7.instantiateMVars t3).1
+
+def mkDiamond : Nat → Expr
+| 0     => m1
+| (n+1) => mkApp f #[mkDiamond n, mkDiamond n]
+
+#eval (mctx7.instantiateMVars (mkDiamond 3)).1
+#eval (mctx10.instantiateMVars (mkDiamond 3)).1
+#eval (mctx7.instantiateMVars (mkDiamond 100)).1.getAppFn
+#eval (mctx10.instantiateMVars (mkDiamond 100)).1.getAppFn
+
+def mctx11 := mctx10.assignDelayed `m6 lctx5 #[α, x, y] m5
+def mctx12 := mctx11.assignExpr `m5 (arrow α α)
+
+def t4 := lctx6.mkLambda #[α, x, y, w] $ mkApp f #[mkApp m4 #[α, x, y], x]
+
+#eval t4
+#eval (mctx9.instantiateMVars t4).1
+#eval (mctx12.instantiateMVars t4).1
+#eval check (mctx9.instantiateMVars t4).1.hasMVar
+#eval check (!((mctx9.instantiateMVars t4).1.hasFVar))
+#eval check (!(mctx12.instantiateMVars t4).1.hasMVar)
+#eval check (!((mctx12.instantiateMVars t4).1.hasFVar))