diff --git a/src/vm/fce.rs b/src/vm/fce.rs
index f2a4fe23..c27acc8e 100644
--- a/src/vm/fce.rs
+++ b/src/vm/fce.rs
@@ -46,13 +46,13 @@ impl FCE {
         let module_abi = module.acquire_abi();
 
         // TODO: introduce a macro for such things
-        let allocate = module_abi.allocate.unwrap();
+        let allocate = module_abi.allocate;
         namespace.insert(
             config.allocate_fn_name.clone(),
             func!(move |size: i32| -> i32 { allocate.call(size).expect("allocate failed") }),
         );
 
-        let invoke = module_abi.invoke.unwrap();
+        let invoke = module_abi.invoke;
         namespace.insert(
             config.invoke_fn_name.clone(),
             func!(move |offset: i32, size: i32| -> i32 {
@@ -60,7 +60,7 @@ impl FCE {
             }),
         );
 
-        let deallocate = module_abi.deallocate.unwrap();
+        let deallocate = module_abi.deallocate;
         namespace.insert(
             config.deallocate_fn_name.clone(),
             func!(move |ptr: i32, size: i32| {
@@ -68,7 +68,7 @@ impl FCE {
             }),
         );
 
-        let store = module_abi.store.unwrap();
+        let store = module_abi.store;
         namespace.insert(
             config.store_fn_name.clone(),
             func!(move |offset: i32, value: i32| {
@@ -76,7 +76,7 @@ impl FCE {
             }),
         );
 
-        let load = module_abi.load.unwrap();
+        let load = module_abi.load;
         namespace.insert(
             config.load_fn_name.clone(),
             func!(move |offset: i32| -> i32 { load.call(offset).expect("load failed") }),
@@ -139,7 +139,7 @@ impl FCEService for FCE {
 
             Entry::Occupied(module) => {
                 if module.get().get_abi_ref_counter() != 0 {
-                    return Err(FCEError::ModuleInUse)
+                    return Err(FCEError::ModuleInUse);
                 }
                 module.remove_entry();
                 Ok(())
diff --git a/src/vm/module/abi.rs b/src/vm/module/abi.rs
index c32792f6..72d316dd 100644
--- a/src/vm/module/abi.rs
+++ b/src/vm/module/abi.rs
@@ -30,17 +30,17 @@ use crate::vm::errors::FCEError;
 ///   5. deallocate(res, strlen(sql)) to clean memory.
 pub(crate) trait ModuleABI {
     /// Allocates a region of memory inside a module. Used for passing argument inside the module.
-    fn allocate(&self, size: i32) -> Result<i32, FCEError>;
+    fn allocate(&mut self, size: i32) -> Result<i32, FCEError>;
 
     /// Deallocates previously allocated memory region.
-    fn deallocate(&self, ptr: i32, size: i32) -> Result<(), FCEError>;
+    fn deallocate(&mut self, ptr: i32, size: i32) -> Result<(), FCEError>;
 
     /// Calls the main entry point of a module called invoke.
-    fn invoke(&self, arg_address: i32, arg_size: i32) -> Result<i32, FCEError>;
+    fn invoke(&mut self, arg_address: i32, arg_size: i32) -> Result<i32, FCEError>;
 
     /// Stores one byte on given address.
-    fn store(&self, address: i32, value: i32) -> Result<(), FCEError>;
+    fn store(&mut self, address: i32, value: i32) -> Result<(), FCEError>;
 
     /// Loads one byte from given address.
-    fn load(&self, address: i32) -> Result<i32, FCEError>;
+    fn load(&mut self, address: i32) -> Result<i32, FCEError>;
 }
diff --git a/src/vm/module/fce_module.rs b/src/vm/module/fce_module.rs
index fe27053d..a4af2d4a 100644
--- a/src/vm/module/fce_module.rs
+++ b/src/vm/module/fce_module.rs
@@ -34,11 +34,11 @@ pub(crate) struct ABI {
     // It is safe to use unwrap() while calling these functions because Option is used here
     // just to allow partially initialization. And all Option fields will contain Some if
     // invoking FCE::new has been succeed.
-    pub(crate) allocate: Option<Func<'static, i32, i32>>,
-    pub(crate) deallocate: Option<Func<'static, (i32, i32), ()>>,
-    pub(crate) invoke: Option<Func<'static, (i32, i32), i32>>,
-    pub(crate) store: Option<Func<'static, (i32, i32)>>,
-    pub(crate) load: Option<Func<'static, i32, i32>>,
+    pub(crate) allocate: Func<'static, i32, i32>,
+    pub(crate) deallocate: Func<'static, (i32, i32), ()>,
+    pub(crate) invoke: Func<'static, (i32, i32), i32>,
+    pub(crate) store: Func<'static, (i32, i32)>,
+    pub(crate) load: Func<'static, i32, i32>,
 }
 
 /// A building block of multi-modules scheme of FCE, represents one module that corresponds
@@ -106,11 +106,11 @@ impl FCEModule {
             );
 
             Ok(ABI {
-                allocate: Some(allocate),
-                deallocate: Some(deallocate),
-                invoke: Some(invoke),
-                store: Some(store),
-                load: Some(load),
+                allocate,
+                deallocate,
+                invoke,
+                store,
+                load,
             })
         }
     }
@@ -219,25 +219,24 @@ impl ModuleAPI for FCEModule {
     }
 }
 
-#[rustfmt::skip]
 impl ModuleABI for FCEModule {
-    fn allocate(&self, size: i32) -> Result<i32, FCEError> {
-        Ok(self.abi.allocate.as_ref().unwrap().call(size)?)
+    fn allocate(&mut self, size: i32) -> Result<i32, FCEError> {
+        Ok(self.abi.allocate.call(size)?)
     }
 
-    fn deallocate(&self, ptr: i32, size: i32) -> Result<(), FCEError> {
-        Ok(self.abi.deallocate.as_ref().unwrap().call(ptr, size)?)
+    fn deallocate(&mut self, ptr: i32, size: i32) -> Result<(), FCEError> {
+        Ok(self.abi.deallocate.call(ptr, size)?)
     }
 
-    fn invoke(&self, arg_address: i32, arg_size: i32) -> Result<i32, FCEError> {
-        Ok(self.abi.invoke.as_ref().unwrap().call(arg_address, arg_size)?)
+    fn invoke(&mut self, arg_address: i32, arg_size: i32) -> Result<i32, FCEError> {
+        Ok(self.abi.invoke.call(arg_address, arg_size)?)
     }
 
-    fn store(&self, address: i32, value: i32) -> Result<(), FCEError> {
-        Ok(self.abi.store.as_ref().unwrap().call(address, value)?)
+    fn store(&mut self, address: i32, value: i32) -> Result<(), FCEError> {
+        Ok(self.abi.store.call(address, value)?)
     }
 
-    fn load(&self, address: i32) -> Result<i32, FCEError> {
-        Ok(self.abi.load.as_ref().unwrap().call(address)?)
+    fn load(&mut self, address: i32) -> Result<i32, FCEError> {
+        Ok(self.abi.load.call(address)?)
     }
 }