diff --git a/lib/spanned_sexp/src/lib.rs b/lib/spanned_sexp/src/lib.rs
index d514af7..9bbe758 100644
--- a/lib/spanned_sexp/src/lib.rs
+++ b/lib/spanned_sexp/src/lib.rs
@@ -53,7 +53,7 @@ pub struct Error {
 
 impl error::Error for Error {
   fn description(&self) -> &str { self.message }
-  fn cause(&self) -> Option<&error::Error> { None }
+  fn cause(&self) -> Option<&dyn error::Error> { None }
 }
 
 /// Since errors are the uncommon case, they're boxed. This keeps the size of