diff --git a/src/program.rs b/src/program.rs
index a16f32fe..e791cafe 100644
--- a/src/program.rs
+++ b/src/program.rs
@@ -296,7 +296,7 @@ macro_rules! declare_builtin_function {
         $arg_d:ident : u64,
         $arg_e:ident : u64,
         $memory_mapping:ident : &mut $MemoryMapping:ty,
-    ) -> Result<u64, $Error:ty> $rust:tt) => {
+    ) -> $Result:ty { $($rust:tt)* }) => {
         $(#[$attr])*
         pub struct $name {}
         impl $name {
@@ -309,8 +309,8 @@ macro_rules! declare_builtin_function {
                 $arg_d: u64,
                 $arg_e: u64,
                 $memory_mapping: &mut $MemoryMapping,
-            ) -> Result<u64, $Error> {
-                $rust
+            ) -> $Result {
+                $($rust)*
             }
             /// VM interface
             #[allow(clippy::too_many_arguments)]