diff --git a/src/domain.rs b/src/domain.rs
index 58f6b6c..b392247 100644
--- a/src/domain.rs
+++ b/src/domain.rs
@@ -3,6 +3,7 @@ use std::borrow::Cow;
 use serde::{Deserialize, Serialize};
 
 use crate::common::{HostAddr, StringValue};
+use crate::Error;
 
 pub mod check;
 pub use check::DomainCheck;
@@ -75,27 +76,31 @@ pub struct DomainContact<'a> {
 }
 
 /// The &lt;period&gt; type for registration, renewal or transfer on domain transactions
-#[derive(Serialize, Debug)]
+#[derive(Clone, Copy, Debug, Serialize)]
 pub struct Period {
     /// The interval (usually 'y' indicating years)
-    unit: String,
+    unit: char,
     /// The length of the registration, renewal or transfer period (usually in years)
     #[serde(rename = "$value")]
-    length: u16,
+    length: u8,
 }
 
 impl Period {
-    /// Creates a new period in years
-    pub fn new(length: u16) -> Period {
-        Period {
-            unit: "y".to_string(),
-            length,
-        }
+    pub fn years(length: u8) -> Result<Self, Error> {
+        Self::new(length, 'y')
     }
 
-    /// Sets the period unit ('y' for years, most commonly)
-    pub fn set_unit(&mut self, unit: &str) {
-        self.unit = unit.to_string();
+    pub fn months(length: u8) -> Result<Self, Error> {
+        Self::new(length, 'm')
+    }
+
+    fn new(length: u8, unit: char) -> Result<Self, Error> {
+        match length {
+            1..=99 => Ok(Period { length, unit }),
+            0 | 100.. => Err(Error::Other(
+                "Period length must be greater than 0 and less than 100".into(),
+            )),
+        }
     }
 }
 
diff --git a/src/domain/create.rs b/src/domain/create.rs
index 5e12fb7..6a7b14f 100644
--- a/src/domain/create.rs
+++ b/src/domain/create.rs
@@ -55,7 +55,7 @@ pub struct DomainCreate<'a> {
 impl<'a> DomainCreate<'a> {
     pub fn new(
         name: &'a str,
-        period: u16,
+        period: Period,
         ns: Option<HostList<'a>>,
         registrant_id: Option<&'a str>,
         auth_password: &'a str,
@@ -65,7 +65,7 @@ impl<'a> DomainCreate<'a> {
             domain: DomainCreateRequestData {
                 xmlns: XMLNS,
                 name: name.into(),
-                period: Period::new(period),
+                period,
                 ns,
                 registrant: registrant_id.map(|id| id.into()),
                 auth_info: DomainAuthInfo::new(auth_password),
@@ -103,7 +103,7 @@ pub struct DomainCreateResponse {
 
 #[cfg(test)]
 mod tests {
-    use super::{DomainContact, DomainCreate, HostList};
+    use super::{DomainContact, DomainCreate, HostList, Period};
     use crate::common::{HostAddr, NoExtension};
     use crate::domain::{HostAttr, HostAttrList, HostObjList};
     use crate::request::Transaction;
@@ -131,7 +131,7 @@ mod tests {
 
         let object = DomainCreate::new(
             "eppdev-1.com",
-            1,
+            Period::years(1).unwrap(),
             None,
             Some("eppdev-contact-3"),
             "epP4uthd#v",
@@ -167,7 +167,7 @@ mod tests {
         let hosts = &["ns1.test.com".into(), "ns2.test.com".into()];
         let object = DomainCreate::new(
             "eppdev-1.com",
-            1,
+            Period::years(1).unwrap(),
             Some(HostList::HostObjList(HostObjList { hosts })),
             Some("eppdev-contact-3"),
             "epP4uthd#v",
@@ -216,7 +216,7 @@ mod tests {
 
         let object = DomainCreate::new(
             "eppdev-2.com",
-            1,
+            Period::years(1).unwrap(),
             Some(HostList::HostAttrList(HostAttrList { hosts })),
             Some("eppdev-contact-3"),
             "epP4uthd#v",
diff --git a/src/domain/renew.rs b/src/domain/renew.rs
index 6177e82..0c6c280 100644
--- a/src/domain/renew.rs
+++ b/src/domain/renew.rs
@@ -14,14 +14,14 @@ impl<'a> Command for DomainRenew<'a> {
 }
 
 impl<'a> DomainRenew<'a> {
-    pub fn new(name: &'a str, current_expiry_date: NaiveDate, years: u16) -> Self {
+    pub fn new(name: &'a str, current_expiry_date: NaiveDate, period: Period) -> Self {
         let exp_date_str = current_expiry_date.format("%Y-%m-%d").to_string().into();
         Self {
             domain: DomainRenewRequestData {
                 xmlns: XMLNS,
                 name: name.into(),
                 current_expiry_date: exp_date_str,
-                period: Period::new(years),
+                period,
             },
         }
     }
@@ -76,7 +76,7 @@ pub struct DomainRenewResponse {
 
 #[cfg(test)]
 mod tests {
-    use super::DomainRenew;
+    use super::{DomainRenew, Period};
     use crate::common::NoExtension;
     use crate::request::Transaction;
     use crate::response::ResultCode;
@@ -88,7 +88,7 @@ mod tests {
         let xml = get_xml("request/domain/renew.xml").unwrap();
 
         let exp_date = NaiveDate::from_ymd(2022, 7, 23);
-        let object = DomainRenew::new("eppdev.com", exp_date, 1);
+        let object = DomainRenew::new("eppdev.com", exp_date, Period::years(1).unwrap());
 
         let serialized =
             <DomainRenew as Transaction<NoExtension>>::serialize_request(&object, None, CLTRID)
diff --git a/src/domain/transfer.rs b/src/domain/transfer.rs
index d248357..fea9e30 100644
--- a/src/domain/transfer.rs
+++ b/src/domain/transfer.rs
@@ -13,11 +13,11 @@ impl<'a> Command for DomainTransfer<'a> {
 }
 
 impl<'a> DomainTransfer<'a> {
-    pub fn new(name: &'a str, years: Option<u16>, auth_password: &'a str) -> Self {
+    pub fn new(name: &'a str, period: Option<Period>, auth_password: &'a str) -> Self {
         Self::build(
             "request",
             name,
-            years.map(Period::new),
+            period,
             Some(DomainAuthInfo::new(auth_password)),
         )
     }
@@ -131,7 +131,7 @@ pub struct DomainTransferResponse {
 
 #[cfg(test)]
 mod tests {
-    use super::DomainTransfer;
+    use super::{DomainTransfer, Period};
     use crate::common::NoExtension;
     use crate::request::Transaction;
     use crate::response::ResultCode;
@@ -141,7 +141,8 @@ mod tests {
     fn request_command() {
         let xml = get_xml("request/domain/transfer_request.xml").unwrap();
 
-        let object = DomainTransfer::new("testing.com", Some(1), "epP4uthd#v");
+        let object =
+            DomainTransfer::new("testing.com", Some(Period::years(1).unwrap()), "epP4uthd#v");
 
         let serialized =
             <DomainTransfer as Transaction<NoExtension>>::serialize_request(&object, None, CLTRID)