diff --git a/melior/src/ir/operation/builder.rs b/melior/src/ir/operation/builder.rs
index fe68add68a..58257f9b70 100644
--- a/melior/src/ir/operation/builder.rs
+++ b/melior/src/ir/operation/builder.rs
@@ -78,7 +78,7 @@ impl<'c> OperationBuilder<'c> {
             mlirOperationStateAddOwnedRegions(
                 &mut self.raw,
                 regions.len() as isize,
-                transmute::<_, Vec<ManuallyDrop<Region>>>(regions).as_ptr() as *const _,
+                transmute::<Vec<Region>, Vec<ManuallyDrop<Region>>>(regions).as_ptr() as *const _,
             )
         }
 
diff --git a/melior/src/pass/external.rs b/melior/src/pass/external.rs
index 4899617bdf..e881d87f4f 100644
--- a/melior/src/pass/external.rs
+++ b/melior/src/pass/external.rs
@@ -10,7 +10,7 @@ use mlir_sys::{
     mlirCreateExternalPass, mlirExternalPassSignalFailure, MlirContext, MlirExternalPass,
     MlirExternalPassCallbacks, MlirLogicalResult, MlirOperation,
 };
-use std::{marker::PhantomData, mem::transmute, ptr::drop_in_place};
+use std::{ffi::c_void, marker::PhantomData, mem::transmute, ptr::drop_in_place};
 
 #[derive(Clone, Copy, Debug)]
 pub struct ExternalPass<'a> {
@@ -185,11 +185,24 @@ pub fn create_external<'c, T: RunExternalPass<'c>>(
             dependent_dialects.len() as isize,
             dependent_dialects.as_ptr() as _,
             MlirExternalPassCallbacks {
-                construct: Some(transmute(callback_construct::<T> as *const ())),
-                destruct: Some(transmute(callback_destruct::<T> as *const ())),
-                initialize: Some(transmute(callback_initialize::<T> as *const ())),
-                run: Some(transmute(callback_run::<T> as *const ())),
-                clone: Some(transmute(callback_clone::<T> as *const ())),
+                construct: Some(transmute::<*const (), unsafe extern "C" fn(*mut c_void)>(
+                    callback_construct::<T> as *const (),
+                )),
+                destruct: Some(transmute::<*const (), unsafe extern "C" fn(*mut c_void)>(
+                    callback_destruct::<T> as *const (),
+                )),
+                initialize: Some(transmute::<
+                    *const (),
+                    unsafe extern "C" fn(MlirContext, *mut c_void) -> MlirLogicalResult,
+                >(callback_initialize::<T> as *const ())),
+                run: Some(transmute::<
+                    *const (),
+                    unsafe extern "C" fn(MlirOperation, MlirExternalPass, *mut c_void),
+                >(callback_run::<T> as *const ())),
+                clone: Some(transmute::<
+                    *const (),
+                    unsafe extern "C" fn(*mut c_void) -> *mut c_void,
+                >(callback_clone::<T> as *const ())),
             },
             Box::into_raw(Box::new(pass)) as _,
         ))