diff --git a/drop-struct-macro-derive/src/lib.rs b/drop-struct-macro-derive/src/lib.rs
index bdddc33..8705fa0 100644
--- a/drop-struct-macro-derive/src/lib.rs
+++ b/drop-struct-macro-derive/src/lib.rs
@@ -11,7 +11,7 @@ struct FieldNameType {
     field_type: proc_macro2::TokenStream,
 }
 
-/// The actual code to free the *const pointers
+/// The actual code to free the *mut pointers
 impl quote::ToTokens for FieldNameType {
     fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
         let field_type = &self.field_type;
@@ -72,13 +72,13 @@ pub fn drop_struct_macro_derive(input: TokenStream) -> TokenStream {
     // A list of fields that should get dropped
     let mut to_be_dropped = Vec::new();
 
-    // Only take *const pointers into account (also not *mut)
+    // Only take *mut pointers into account (also not *mut)
     match ast.data {
         syn::Data::Struct(ref data_struct) => {
             if let syn::Fields::Named(ref fields_named) = data_struct.fields {
                 for field in fields_named.named.iter() {
                     if let syn::Type::Ptr(ref type_ptr) = field.ty {
-                        if type_ptr.const_token.is_some() {
+                        if type_ptr.mutability.is_some() {
                             if let syn::Type::Path(ref type_path) = *type_ptr.elem {
                                 let field_name = field.ident.clone().unwrap().to_string();
                                 let field_type = type_path.path.clone().into_token_stream();
diff --git a/ffi-toolkit/src/lib.rs b/ffi-toolkit/src/lib.rs
index 870ded9..19b351a 100644
--- a/ffi-toolkit/src/lib.rs
+++ b/ffi-toolkit/src/lib.rs
@@ -16,18 +16,18 @@ pub enum FCPResponseStatus {
 /// All FFI responses need to implement this trait in order to be able to use `catch_panic()`
 pub trait CodeAndMessage {
     /// Set the status code and error message
-    fn set_error(&mut self, code_and_message: (FCPResponseStatus, *const libc::c_char));
+    fn set_error(&mut self, code_and_message: (FCPResponseStatus, *mut libc::c_char));
 }
 
 /// A simple macro to create implementations for the `CodeAndMessage` trait
 ///
 /// The only requirement is that the response has an `status_code: FCPResponseStatus` and
-/// `error_msg: *const libc::c_char` field.
+/// `error_msg: *mut libc::c_char` field.
 #[macro_export]
 macro_rules! code_and_message_impl {
     { $response:ty } => {
         impl CodeAndMessage for $response {
-            fn set_error(&mut self, (code, message): (FCPResponseStatus, *const libc::c_char)) {
+            fn set_error(&mut self, (code, message): (FCPResponseStatus, *mut libc::c_char)) {
                 self.status_code = code;
                 self.error_msg = message;
             }
diff --git a/ffi-toolkit/tests/catch_panic_response.rs b/ffi-toolkit/tests/catch_panic_response.rs
index c44d2b2..2113838 100644
--- a/ffi-toolkit/tests/catch_panic_response.rs
+++ b/ffi-toolkit/tests/catch_panic_response.rs
@@ -13,7 +13,7 @@ use ffi_toolkit::{
 #[derive(DropStructMacro)]
 pub struct BasicResponse {
     pub status_code: FCPResponseStatus,
-    pub error_msg: *const libc::c_char,
+    pub error_msg: *mut libc::c_char,
     pub is_valid: bool,
 }
 
@@ -21,7 +21,7 @@ impl Default for BasicResponse {
     fn default() -> Self {
         BasicResponse {
             status_code: FCPResponseStatus::FCPNoError,
-            error_msg: ptr::null(),
+            error_msg: ptr::null_mut(),
             is_valid: false,
         }
     }
@@ -55,7 +55,7 @@ fn does_not_panic() {
         let response = fn_does_not_panic();
         assert!((*response).is_valid);
         assert_eq!((*response).status_code, FCPResponseStatus::FCPNoError);
-        assert_eq!((*response).error_msg, ptr::null());
+        assert!((*response).error_msg.is_null());
     }
 }
 
@@ -66,7 +66,7 @@ fn does_not_panic_with_catch_panic_response() {
         let response = fn_does_not_panic_with_catch_panic();
         assert!((*response).is_valid);
         assert_eq!((*response).status_code, FCPResponseStatus::FCPNoError);
-        assert_eq!((*response).error_msg, ptr::null());
+        assert!((*response).error_msg.is_null());
     }
 }