diff --git a/lib/cretonne/src/context.rs b/lib/cretonne/src/context.rs
index fba2cd2cc3..54fce4b84a 100644
--- a/lib/cretonne/src/context.rs
+++ b/lib/cretonne/src/context.rs
@@ -88,7 +88,9 @@ impl Context {
         self.verify_if(isa)?;
 
         self.compute_cfg();
-        self.preopt(isa)?;
+        if isa.flags().opt_level() != OptLevel::Fastest {
+            self.preopt(isa)?;
+        }
         self.legalize(isa)?;
         if isa.flags().opt_level() == OptLevel::Best {
             self.compute_domtree();