diff --git a/lib/cretonne/src/isa/mod.rs b/lib/cretonne/src/isa/mod.rs
index f6c95edec8..78a7e79176 100644
--- a/lib/cretonne/src/isa/mod.rs
+++ b/lib/cretonne/src/isa/mod.rs
@@ -177,7 +177,7 @@ pub trait TargetIsa {
         ctrl_typevar: ir::Type,
     ) -> Result<Encoding, Legalize> {
         let mut iter = self.legal_encodings(dfg, inst, ctrl_typevar);
-        iter.next().ok_or_else(|| iter.legalize().into())
+        iter.next().ok_or_else(|| iter.legalize())
     }
 
     /// Get a data structure describing the instruction encodings in this ISA.