diff --git a/src/rstd/singular.rs b/src/rstd/singular.rs
index 95a542e..1c45c81 100644
--- a/src/rstd/singular.rs
+++ b/src/rstd/singular.rs
@@ -58,6 +58,8 @@ impl Display for SingularError {
     }
 }
 
+impl Error for SingularError {}
+
 impl<'a, Ctx: Context<'a>> SingularResolver<'a, Ctx> {
     pub fn from_mentionable<A: Mentionable<'a, Ctx>>(a: &A) -> Self {
         let mut points = Vec::new();