diff --git a/src/Lean/DocString.lean b/src/Lean/DocString.lean
index 70d241e5a2..901e260ff9 100644
--- a/src/Lean/DocString.lean
+++ b/src/Lean/DocString.lean
@@ -95,6 +95,7 @@ def getDocStringText [Monad m] [MonadError m] [MonadRef m] (stx : TSyntax `Lean.
 def TSyntax.getDocString (stx : TSyntax `Lean.Parser.Command.docComment) : String :=
   match stx.raw[1] with
   | Syntax.atom _ val => val.extract 0 (val.endPos - ⟨2⟩)
+  | Syntax.missing    => ""
   | _                 => panic! s!"unexpected doc string\n{stx.raw[1]}"
 
 end Lean