@@ -448,9 +448,7 @@ public readonly record struct NpgsqlInet
 
     public NpgsqlInet(IPAddress address, byte netmask)
     {
-        if (address.AddressFamily != AddressFamily.InterNetwork && address.AddressFamily != AddressFamily.InterNetworkV6)
-            throw new ArgumentException("Only IPAddress of InterNetwork or InterNetworkV6 address families are accepted", nameof(address));
-
+        CheckAddressFamily(address);
         Address = address;
         Netmask = netmask;
     }
@@ -461,12 +459,23 @@ public NpgsqlInet(IPAddress address)
     }
 
     public NpgsqlInet(string addr)
-        => (Address, Netmask) = addr.Split('/') switch
+    {
+        switch (addr.Split('/'))
         {
-            { Length: 2 } segments => (IPAddress.Parse(segments[0]), byte.Parse(segments[1])),
-            { Length: 1 } segments => (IPAddress.Parse(segments[0]), (byte)32),
-            _ => throw new FormatException("Invalid number of parts in CIDR specification")
-        };
+        case { Length: 2 } segments:
+            (Address, Netmask) = (IPAddress.Parse(segments[0]), byte.Parse(segments[1]));
+            break;
+        case { Length: 1 } segments:
+            var ipAddr = IPAddress.Parse(segments[0]);
+            CheckAddressFamily(ipAddr);
+            (Address, Netmask) = (
+                ipAddr,
+                ipAddr.AddressFamily == AddressFamily.InterNetworkV6 ? (byte)128 : (byte)32);
+            break;
+        default:
+            throw new FormatException("Invalid number of parts in CIDR specification");
+        }
+    }
 
     public override string ToString()
         => (Address.AddressFamily == AddressFamily.InterNetwork && Netmask == 32) ||
@@ -485,6 +494,12 @@ public void Deconstruct(out IPAddress address, out byte netmask)
         address = Address;
         netmask = Netmask;
     }
+
+    static void CheckAddressFamily(IPAddress address)
+    {
+        if (address.AddressFamily != AddressFamily.InterNetwork && address.AddressFamily != AddressFamily.InterNetworkV6)
+            throw new ArgumentException("Only IPAddress of InterNetwork or InterNetworkV6 address families are accepted", nameof(address));
+    }
 }
 
 /// <summary>
 
@@ -209,4 +209,43 @@ public void NpgsqlInet()
         var v = new NpgsqlInet(IPAddress.Parse("2001:1db8:85a3:1142:1000:8a2e:1370:7334"), 32);
         Assert.That(v.ToString(), Is.EqualTo("2001:1db8:85a3:1142:1000:8a2e:1370:7334/32"));
     }
+
+    [Test]
+    public void NpgsqlInet_parse_ipv4()
+    {
+        var ipv4 = new NpgsqlInet("192.168.1.1/8");
+        Assert.That(ipv4.Address, Is.EqualTo(IPAddress.Parse("192.168.1.1")));
+        Assert.That(ipv4.Netmask, Is.EqualTo(8));
+
+        ipv4 = new NpgsqlInet("192.168.1.1/32");
+        Assert.That(ipv4.Address, Is.EqualTo(IPAddress.Parse("192.168.1.1")));
+        Assert.That(ipv4.Netmask, Is.EqualTo(32));
+    }
+
+    [Test]
+    [IssueLink("https://github.com/npgsql/npgsql/issues/5638")]
+    public void NpgsqlInet_parse_ipv6()
+    {
+        var ipv6 = new NpgsqlInet("2001:0000:130F:0000:0000:09C0:876A:130B/32");
+        Assert.That(ipv6.Address, Is.EqualTo(IPAddress.Parse("2001:0000:130F:0000:0000:09C0:876A:130B")));
+        Assert.That(ipv6.Netmask, Is.EqualTo(32));
+
+        ipv6 = new NpgsqlInet("2001:0000:130F:0000:0000:09C0:876A:130B");
+        Assert.That(ipv6.Address, Is.EqualTo(IPAddress.Parse("2001:0000:130F:0000:0000:09C0:876A:130B")));
+        Assert.That(ipv6.Netmask, Is.EqualTo(128));
+    }
+
+    [Test]
+    public void NpgsqlInet_ToString_ipv4()
+    {
+        Assert.That(new NpgsqlInet("192.168.1.1/8").ToString(), Is.EqualTo("192.168.1.1/8"));
+        Assert.That(new NpgsqlInet("192.168.1.1/32").ToString(), Is.EqualTo("192.168.1.1"));
+    }
+
+    [Test]
+    public void NpgsqlInet_ToString_ipv6()
+    {
+        Assert.That(new NpgsqlInet("2001:0:130f::9c0:876a:130b/32").ToString(), Is.EqualTo("2001:0:130f::9c0:876a:130b/32"));
+        Assert.That(new NpgsqlInet("2001:0:130f::9c0:876a:130b/128").ToString(), Is.EqualTo("2001:0:130f::9c0:876a:130b"));
+    }
 }