diff --git a/src/common.rs b/src/common.rs
index 7016990..17ac193 100644
--- a/src/common.rs
+++ b/src/common.rs
@@ -32,15 +32,12 @@ impl Error for IpNetworkError {
     }
 }
 
-pub fn cidr_parts(cidr: &str) -> Result<(&str, &str), IpNetworkError> {
+pub fn cidr_parts(cidr: &str) -> Result<(&str, Option<&str>), IpNetworkError> {
     let parts = cidr.split('/').collect::<Vec<&str>>();
     if parts.len() == 1 {
-        Err(IpNetworkError::InvalidCidrFormat(format!(
-            "CIDR must contain '/': {}",
-            cidr
-        )))
+        Ok((parts[0], None))
     } else if parts.len() == 2 {
-        Ok((parts[0], parts[1]))
+        Ok((parts[0], Some(parts[1])))
     } else {
         Err(IpNetworkError::InvalidCidrFormat(format!(
             "CIDR must contain a single '/': {}",
diff --git a/src/ipv4.rs b/src/ipv4.rs
index 76af8b4..e0fd721 100644
--- a/src/ipv4.rs
+++ b/src/ipv4.rs
@@ -57,6 +57,8 @@ impl Ipv4Network {
     /// use std::net::Ipv4Addr;
     /// use ipnetwork::Ipv4Network;
     ///
+    /// let net: Ipv4Network = "127.0.0.0".parse().unwrap();
+    /// assert_eq!(net.mask(), Ipv4Addr::new(255, 255, 255, 255));
     /// let net: Ipv4Network = "127.0.0.0/16".parse().unwrap();
     /// assert_eq!(net.mask(), Ipv4Addr::new(255, 255, 0, 0));
     /// ```
@@ -190,7 +192,10 @@ impl FromStr for Ipv4Network {
     fn from_str(s: &str) -> Result<Ipv4Network, IpNetworkError> {
         let (addr_str, prefix_str) = cidr_parts(s)?;
         let addr = parse_addr(addr_str)?;
-        let prefix = parse_prefix(prefix_str, IPV4_BITS)?;
+        let prefix = match prefix_str {
+            Some(v) => parse_prefix(v, IPV4_BITS)?,
+            None => IPV4_BITS,
+        };
         Ipv4Network::new(addr, prefix)
     }
 }
@@ -276,6 +281,13 @@ mod test {
         assert_eq!(cidr.prefix(), 32);
     }
 
+    #[test]
+    fn parse_v4_noprefix() {
+        let cidr: Ipv4Network = "127.0.0.0".parse().unwrap();
+        assert_eq!(cidr.ip(), Ipv4Addr::new(127, 0, 0, 0));
+        assert_eq!(cidr.prefix(), 32);
+    }
+
     #[test]
     fn parse_v4_fail_addr() {
         let cidr: Option<Ipv4Network> = "10.a.b/8".parse().ok();
diff --git a/src/ipv6.rs b/src/ipv6.rs
index 850654f..711423e 100644
--- a/src/ipv6.rs
+++ b/src/ipv6.rs
@@ -106,6 +106,8 @@ impl Ipv6Network {
     /// use std::net::Ipv6Addr;
     /// use ipnetwork::Ipv6Network;
     ///
+    /// let net: Ipv6Network = "ff01::0".parse().unwrap();
+    /// assert_eq!(net.mask(), Ipv6Addr::new(0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff));
     /// let net: Ipv6Network = "ff01::0/32".parse().unwrap();
     /// assert_eq!(net.mask(), Ipv6Addr::new(0xffff, 0xffff, 0, 0, 0, 0, 0, 0));
     /// ```
@@ -170,7 +172,10 @@ impl FromStr for Ipv6Network {
         let (addr_str, prefix_str) = cidr_parts(s)?;
         let addr = Ipv6Addr::from_str(addr_str)
             .map_err(|_| IpNetworkError::InvalidAddr(addr_str.to_string()))?;
-        let prefix = parse_prefix(prefix_str, IPV6_BITS)?;
+        let prefix = match prefix_str {
+            Some(v) => parse_prefix(v, IPV6_BITS)?,
+            None => IPV6_BITS,
+        };
         Ipv6Network::new(addr, prefix)
     }
 }
@@ -277,6 +282,13 @@ mod test {
         assert_eq!(cidr.prefix(), 64);
     }
 
+    #[test]
+    fn parse_v6_noprefix() {
+        let cidr: Ipv6Network = "::1".parse().unwrap();
+        assert_eq!(cidr.ip(), Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1));
+        assert_eq!(cidr.prefix(), 128);
+    }
+
     #[test]
     fn parse_v6_fail_addr() {
         let cidr: Option<Ipv6Network> = "2001::1::/8".parse().ok();
diff --git a/src/lib.rs b/src/lib.rs
index e3b6925..21f99df 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -62,7 +62,10 @@ impl IpNetwork {
     /// ```
     /// use ipnetwork::IpNetwork;
     ///
+    /// assert_eq!(IpNetwork::V4("10.9.0.1".parse().unwrap()).prefix(), 32u8);
     /// assert_eq!(IpNetwork::V4("10.9.0.32/16".parse().unwrap()).prefix(), 16u8);
+    ///
+    /// assert_eq!(IpNetwork::V6("ff01::0".parse().unwrap()).prefix(), 128u8);
     /// assert_eq!(IpNetwork::V6("ff01::0/32".parse().unwrap()).prefix(), 32u8);
     /// ```
     pub fn prefix(&self) -> u8 {
@@ -80,8 +83,13 @@ impl IpNetwork {
     /// use ipnetwork::IpNetwork;
     /// use std::net::{Ipv4Addr, Ipv6Addr};
     ///
+    /// let v4_net: IpNetwork = "10.9.0.1".parse().unwrap();
+    /// assert_eq!(v4_net.mask(), Ipv4Addr::new(255, 255, 255, 255));
     /// let v4_net: IpNetwork = "10.9.0.32/16".parse().unwrap();
     /// assert_eq!(v4_net.mask(), Ipv4Addr::new(255, 255, 0, 0));
+    ///
+    /// let v6_net: IpNetwork = "ff01::0".parse().unwrap();
+    /// assert_eq!(v6_net.mask(), Ipv6Addr::new(0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff, 0xffff));
     /// let v6_net: IpNetwork = "ff01::0/32".parse().unwrap();
     /// assert_eq!(v6_net.mask(), Ipv6Addr::new(0xffff, 0xffff, 0, 0, 0, 0, 0, 0));
     ///```