diff --git a/libchisel/src/binaryenopt.rs b/libchisel/src/binaryenopt.rs
index 7236e7a..94fb84c 100644
--- a/libchisel/src/binaryenopt.rs
+++ b/libchisel/src/binaryenopt.rs
@@ -40,7 +40,7 @@ impl ModuleConfig for BinaryenOptimiser {
         if let Some(preset) = config.get("preset") {
             BinaryenOptimiser::with_preset(preset)
         } else {
-            Err(ModuleError::NotSupported)
+            Err(ModuleError::MissingConfigKey("preset"))
         }
     }
 }
@@ -55,7 +55,7 @@ impl ModulePreset for BinaryenOptimiser {
             "O4" => Ok(BinaryenOptimiser::O4),
             "Os" => Ok(BinaryenOptimiser::Os),
             "Oz" => Ok(BinaryenOptimiser::Oz),
-            _ => Err(ModuleError::NotSupported),
+            _ => Err(ModuleError::InvalidConfigValue("preset", preset)),
         }
     }
 }