diff --git a/internal/generator/method/method.go b/internal/generator/method/method.go
index f776237..e94528a 100644
--- a/internal/generator/method/method.go
+++ b/internal/generator/method/method.go
@@ -226,6 +226,16 @@ func toType(t types.Type, variadic bool) (jen.Code, error) {
 		return jen.Index().Add(elemType), nil
 	case named:
 		return jen.Id(v.Name()), nil
+	case *types.Map:
+		keyType, err := toType(v.Key(), false)
+		if err != nil {
+			return nil, err
+		}
+		elemType, err := toType(v.Elem(), false)
+		if err != nil {
+			return nil, err
+		}
+		return jen.Map(keyType).Add(elemType), nil
 	default:
 		return nil, fmt.Errorf("type not handled: %T", v)
 	}
diff --git a/internal/generator/method/method_test.go b/internal/generator/method/method_test.go
index cf10a92..99db205 100644
--- a/internal/generator/method/method_test.go
+++ b/internal/generator/method/method_test.go
@@ -154,6 +154,23 @@ func TestNewMethod(t *testing.T) {
 				ReturnTypes:           []jen.Code{jen.Id("interface{}")},
 			},
 		},
+		{
+			name: "Fn(arg map[string]interface{}) map[string]int",
+			args: args{
+				name: "Fn",
+				signature: types.NewSignature(nil,
+					types.NewTuple(types.NewVar(token.NoPos, nil, "arg", types.NewMap(types.Typ[types.String], types.NewInterfaceType(nil, nil)))),
+					types.NewTuple(types.NewVar(token.NoPos, nil, "", types.NewMap(types.Typ[types.String], types.Typ[types.Int]))),
+					false),
+			},
+			want: &method.Method{
+				Name:                  "Fn",
+				HasContext:            false,
+				ParameterNames:        []string{"arg0"},
+				ParametersNameAndType: []jen.Code{jen.Id("arg0").Add(jen.Map(jen.Id("string")).Add(jen.Id("interface{}")))},
+				ReturnTypes:           []jen.Code{jen.Map(jen.Id("string")).Add(jen.Id("int"))},
+			},
+		},
 	}
 
 	for _, tt := range tests {