diff --git a/CHANGELOG.md b/CHANGELOG.md
index a2c6b94..ba03899 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [unreleased]
 
+### Changed
+
+- Moved register value mask definitions from reg module to field value impl.
+
 ## [0.3.0] - 2025-03-27
 
 ### Added
diff --git a/src/generator/codegen_register.rs b/src/generator/codegen_register.rs
index 62bfef0..b54e4a9 100644
--- a/src/generator/codegen_register.rs
+++ b/src/generator/codegen_register.rs
@@ -232,11 +232,11 @@ fn generate_single_field(
             }
         }
         FieldType::CustomValue(values) => {
-            let additional =
+            let values_enum_masks =
                 generate_custom_values_const_enumdef(&base_type, &snake_case_name, values);
             quote! {
                 const #mask_name: #base_type = #mask_val;
-                #additional
+                #values_enum_masks
             }
         }
     };
@@ -320,13 +320,8 @@ fn generate_single_ux_field(
     (code_getter, code_setter)
 }
 
-fn custom_value_const_name(field_name: &Ident, value_name: &str) -> Ident {
-    util::parse_to_ident(&format!(
-        "{}_VAL_{}",
-        field_name.to_string().to_shouty_snake_case(),
-        value_name.to_shouty_snake_case()
-    ))
-    .unwrap()
+fn custom_value_const_name(value_name: &str) -> Ident {
+    util::parse_to_ident(&format!("VAL_{}", value_name.to_shouty_snake_case())).unwrap()
 }
 
 /// Generate const var and value enum definition.
@@ -338,7 +333,7 @@ fn generate_custom_values_const_enumdef(
     values: &[Value],
 ) -> TokenStream {
     let consts = values.iter().map(|value| {
-        let const_name = custom_value_const_name(field_name, &value.name);
+        let const_name = custom_value_const_name(&value.name);
         let val = value.data;
         quote! {
             const #const_name: #base_type = #val;
@@ -356,10 +351,13 @@ fn generate_custom_values_const_enumdef(
         util::parse_to_ident(&field_name.to_string().to_upper_camel_case()).unwrap();
 
     quote! {
-        #(#consts)*
         pub enum #value_enum_name {
             #(#variants),*
         }
+
+        impl #value_enum_name {
+            #(#consts)*
+        }
     }
 }
 
@@ -376,14 +374,14 @@ fn generate_single_custom_values_field(
     let (getter_match_arms, setter_match_arms): (Vec<_>, Vec<_>) = values
         .iter()
         .map(|value| {
-            let const_name = custom_value_const_name(&snake_case_name, &value.name);
+            let const_name = custom_value_const_name(&value.name);
             let variant_name = util::parse_to_ident(&value.name.to_upper_camel_case()).unwrap();
             (
                 quote! {
-                    #const_name => #value_enum_name::#variant_name
+                    #value_enum_name::#const_name => #value_enum_name::#variant_name
                 },
                 quote! {
-                     #value_enum_name::#variant_name => #const_name
+                    #value_enum_name::#variant_name => #value_enum_name::#const_name
                 },
             )
         })
@@ -596,14 +594,14 @@ fn generate_multiple_custom_values_field(
     let (getter_match_arms, setter_match_arms): (Vec<_>, Vec<_>) = values
         .iter()
         .map(|value| {
-            let const_name = custom_value_const_name(&snake_case_name, &value.name);
+            let const_name = custom_value_const_name(&value.name);
             let variant_name = util::parse_to_ident(&value.name.to_upper_camel_case()).unwrap();
             (
                 quote! {
-                    #const_name => #value_enum_name::#variant_name
+                    #value_enum_name::#const_name => #value_enum_name::#variant_name
                 },
                 quote! {
-                     #value_enum_name::#variant_name => #const_name
+                    #value_enum_name::#variant_name => #value_enum_name::#const_name
                 },
             )
         })