diff --git a/codegen/astgen/v3/common.go b/codegen/astgen/v3/common.go
index ec87380..64e6114 100644
--- a/codegen/astgen/v3/common.go
+++ b/codegen/astgen/v3/common.go
@@ -216,6 +216,7 @@ func (c *codeGenAst) getTemplates(
 					RawType:      field.String(),
 					IsOptional:   isOptional,
 					IsEnum:       c.isEnumType(typeExtracted, pkg),
+					IsBytes:      model.BytesFieldNames[fieldExtracted],
 					IsBytesHex:   model.BytesHexFieldNames[fieldExtracted],
 					IsUint32:     model.Uint32FieldNames[fieldExtracted],
 					IsUint32List: model.Uint32ListFieldNames[fieldExtracted],
@@ -438,6 +439,7 @@ func (c *codeGenAst) getDataTypes(pkg *daml.Package, module *daml.Module, module
 					Type:         typeExtracted,
 					RawType:      field.String(),
 					IsOptional:   isOptional,
+					IsBytes:      model.BytesFieldNames[fieldExtracted],
 					IsBytesHex:   model.BytesHexFieldNames[fieldExtracted],
 					IsUint32:     model.Uint32FieldNames[fieldExtracted],
 					IsUint32List: model.Uint32ListFieldNames[fieldExtracted],
@@ -455,6 +457,7 @@ func (c *codeGenAst) getDataTypes(pkg *daml.Package, module *daml.Module, module
 					Type:         typeExtracted,
 					RawType:      field.String(),
 					IsOptional:   true,
+					IsBytes:      model.BytesFieldNames[fieldExtracted],
 					IsBytesHex:   model.BytesHexFieldNames[fieldExtracted],
 					IsUint32:     model.Uint32FieldNames[fieldExtracted],
 					IsUint32List: model.Uint32ListFieldNames[fieldExtracted],
diff --git a/codegen/model/template.go b/codegen/model/template.go
index bd7670e..192a6f2 100644
--- a/codegen/model/template.go
+++ b/codegen/model/template.go
@@ -29,6 +29,7 @@ type TmplField struct {
 	RawType      string
 	IsOptional   bool
 	IsEnum       bool
+	IsBytes      bool // True if field should use uint8 length prefix (hex:"bytes" tag)
 	IsBytesHex   bool // True if field should use uint16 length prefix (hex:"bytes16" tag)
 	IsUint32     bool // True if INT64 field should encode as 4-byte uint32 (hex:"uint32" tag)
 	IsUint32List bool // True if []INT64 field should encode with 4-byte uint32 elements (hex:"[]uint32" tag)
diff --git a/codegen/model/types.go b/codegen/model/types.go
index 20197c6..7f3f007 100644
--- a/codegen/model/types.go
+++ b/codegen/model/types.go
@@ -68,6 +68,18 @@ func (t BytesHex) IsBytesHex() bool {
 	return true
 }
 
+// ** Custom Bytes Length Mapping **
+
+// The Daml compiler erases type synonyms. When you define a field as BytesHex in Daml,
+// the compiler expands it to its underlying type (Text) in the compiled Daml-LF output.
+// By the time go-daml parses the .dalf files, all it sees is
+// signerAddress: Text
+// operationData: Text
+// root: Text
+// There's no way to distinguish which Text fields were originally BytesHex and require special encoding.
+// The hardcoded maps (BytesFieldNames, BytesHexFieldNames) work around this limitation by explicitly listing
+// field names that need hex encoding tags.
+
 // BytesHexFieldNames contains field names that should use uint16 length prefix
 // encoding (hex:"bytes16" tag) instead of the default uint8 length prefix.
 //
@@ -87,6 +99,21 @@ var BytesHexFieldNames = map[string]bool{
 	"salt":          true,
 }
 
+// BytesFieldNames contains field names that should use uint8 length prefix
+// encoding (hex:"bytes" tag). These are fixed-size hex fields ≤255 bytes.
+//
+// From MCMS/CCIP contracts:
+// - signerAddress: EVM signer address (20 bytes)
+// - chainFamilySelector: Chain family selector (4 bytes)
+// - root: Merkle root hash (32 bytes)
+// - newRoot: New merkle root hash (32 bytes)
+var BytesFieldNames = map[string]bool{
+	"signerAddress":       true,
+	"chainFamilySelector": true,
+	"root":                true,
+	"newRoot":             true,
+}
+
 // Uint32FieldNames contains field names where INT64 should encode as 4-byte uint32.
 // This matches the Daml MCMS/Codec.daml encoding which uses encodeUint32 for these fields.
 //
diff --git a/codegen/source.go.tmpl b/codegen/source.go.tmpl
index f5026a3..5b933dc 100644
--- a/codegen/source.go.tmpl
+++ b/codegen/source.go.tmpl
@@ -301,7 +301,7 @@ var _ types.ENUM = {{capitalise .Name}}("")
 // {{capitalise .Name}} is a {{.RawType}} type
 type {{capitalise .Name}} struct {
 	{{- range $field := .Fields}}
-	{{capitalise $field.Name}} {{$field.Type.GoType}} `json:"{{$field.Name}}"{{if $field.IsOptional}} hex:"optional"{{else if $field.IsBytesHex}} hex:"bytes16"{{else if $field.IsUint32}} hex:"uint32"{{else if $field.IsUint32List}} hex:"[]uint32"{{end}}`
+	{{capitalise $field.Name}} {{$field.Type.GoType}} `json:"{{$field.Name}}"{{if $field.IsOptional}} hex:"optional"{{else if $field.IsBytes}} hex:"bytes"{{else if $field.IsBytesHex}} hex:"bytes16"{{else if $field.IsUint32}} hex:"uint32"{{else if $field.IsUint32List}} hex:"[]uint32"{{end}}`
 	{{- end}}
 }
 
@@ -359,7 +359,7 @@ func (t *{{capitalise .Name}}) UnmarshalHex(data string) error {
 type {{capitalise .Name}}MCMSParams struct {
 {{- range .Fields}}
 {{- if not (isCallerField .Name)}}
-	{{capitalise .Name}} {{.Type.GoType}} `json:"{{.Name}}"{{if .IsOptional}} hex:"optional"{{else if .IsBytesHex}} hex:"bytes16"{{else if .IsUint32}} hex:"uint32"{{else if .IsUint32List}} hex:"[]uint32"{{end}}`
+	{{capitalise .Name}} {{.Type.GoType}} `json:"{{.Name}}"{{if .IsOptional}} hex:"optional"{{else if .IsBytes}} hex:"bytes"{{else if .IsBytesHex}} hex:"bytes16"{{else if .IsUint32}} hex:"uint32"{{else if .IsUint32List}} hex:"[]uint32"{{end}}`
 {{- end}}
 {{- end}}
 }