diff --git a/src/Lean/Environment.lean b/src/Lean/Environment.lean
index 8aeb8a2641..209c4ea06c 100644
--- a/src/Lean/Environment.lean
+++ b/src/Lean/Environment.lean
@@ -659,7 +659,7 @@ private def throwUnexpectedType {α} (typeName : Name) (constName : Name) : Exce
     This function is still unsafe because it cannot guarantee that `typeName` is in fact the name of the type `α`. -/
 unsafe def evalConstCheck (α) (env : Environment) (opts : Options) (typeName : Name) (constName : Name) : ExceptT String Id α :=
   match env.find? constName with
-  | none      => throw ("unknow constant '" ++ toString constName ++ "'")
+  | none      => throw ("unknown constant '" ++ toString constName ++ "'")
   | some info =>
     match info.type with
     | Expr.const c _ _ =>