diff --git a/build.rs b/build.rs
index c478485..44fd098 100644
--- a/build.rs
+++ b/build.rs
@@ -23,6 +23,9 @@ fn main() -> Result<(), Box<dyn Error>> {
         .define("VB_LITTLE_ENDIAN", None)
         .define("VB_SIGNED_PROPAGATE", None)
         .define("VB_DIV_GENERIC", None)
+        .define("VB_DIRECT_EXECUTE", "on_execute")
+        .define("VB_DIRECT_READ", "on_read")
+        .define("VB_DIRECT_WRITE", "on_write")
         .file(Path::new("shrooms-vb-core/core/vb.c"))
         .compile("vb");
 
diff --git a/src/emulator/shrooms_vb_core.rs b/src/emulator/shrooms_vb_core.rs
index c6952cd..b27b9d8 100644
--- a/src/emulator/shrooms_vb_core.rs
+++ b/src/emulator/shrooms_vb_core.rs
@@ -178,6 +178,7 @@ extern "C" fn on_frame(sim: *mut VB) -> c_int {
     1
 }
 
+#[no_mangle]
 extern "C" fn on_execute(sim: *mut VB, address: u32, _code: *const u16, _length: c_int) -> c_int {
     // SAFETY: the *mut VB owns its userdata.
     // There is no way for the userdata to be null or otherwise invalid.
@@ -201,6 +202,7 @@ extern "C" fn on_execute(sim: *mut VB, address: u32, _code: *const u16, _length:
     }
 }
 
+#[no_mangle]
 extern "C" fn on_read(
     sim: *mut VB,
     address: u32,
@@ -226,6 +228,7 @@ extern "C" fn on_read(
     0
 }
 
+#[no_mangle]
 extern "C" fn on_write(
     sim: *mut VB,
     address: u32,