diff --git a/src/libraries/System.Net.Primitives/src/System/Net/IPAddress.cs b/src/libraries/System.Net.Primitives/src/System/Net/IPAddress.cs
index 48f424407b400c..cf45264cf0d30d 100644
--- a/src/libraries/System.Net.Primitives/src/System/Net/IPAddress.cs
+++ b/src/libraries/System.Net.Primitives/src/System/Net/IPAddress.cs
@@ -86,6 +86,20 @@ private set
             }
         }
 
+        internal uint PrivateIPv4Address
+        {
+            get
+            {
+                Debug.Assert(IsIPv4 || IsIPv4MappedToIPv6);
+                if (IsIPv4)
+                {
+                    return _addressOrScopeId;
+                }
+                uint address = (uint)_numbers[6] << 16 | (uint)_numbers[7];
+                return (uint)HostToNetworkOrder(unchecked((int)address));
+            }
+        }
+
         private uint PrivateScopeId
         {
             get
diff --git a/src/libraries/System.Net.Primitives/src/System/Net/IPNetwork.cs b/src/libraries/System.Net.Primitives/src/System/Net/IPNetwork.cs
index 1c3a3acd42932e..b57cc93126aa1e 100644
--- a/src/libraries/System.Net.Primitives/src/System/Net/IPNetwork.cs
+++ b/src/libraries/System.Net.Primitives/src/System/Net/IPNetwork.cs
@@ -84,7 +84,7 @@ public bool Contains(IPAddress address)
         {
             ArgumentNullException.ThrowIfNull(address);
 
-            if (address.AddressFamily != BaseAddress.AddressFamily)
+            if (address.AddressFamily != BaseAddress.AddressFamily && (BaseAddress.AddressFamily != AddressFamily.InterNetwork || !address.IsIPv4MappedToIPv6))
             {
                 return false;
             }
@@ -95,7 +95,7 @@ public bool Contains(IPAddress address)
                 return true;
             }
 
-            if (address.AddressFamily == AddressFamily.InterNetwork)
+            if (address.AddressFamily == AddressFamily.InterNetwork || address.IsIPv4MappedToIPv6)
             {
                 uint mask = uint.MaxValue << (32 - PrefixLength);
                 if (BitConverter.IsLittleEndian)
@@ -103,7 +103,7 @@ public bool Contains(IPAddress address)
                     mask = BinaryPrimitives.ReverseEndianness(mask);
                 }
 
-                return BaseAddress.PrivateAddress == (address.PrivateAddress & mask);
+                return BaseAddress.PrivateIPv4Address == (address.PrivateIPv4Address & mask);
             }
             else
             {
diff --git a/src/libraries/System.Net.Primitives/tests/FunctionalTests/IPNetworkTest.cs b/src/libraries/System.Net.Primitives/tests/FunctionalTests/IPNetworkTest.cs
index 6688b7a7864343..4c56e2d709e346 100644
--- a/src/libraries/System.Net.Primitives/tests/FunctionalTests/IPNetworkTest.cs
+++ b/src/libraries/System.Net.Primitives/tests/FunctionalTests/IPNetworkTest.cs
@@ -151,10 +151,12 @@ public void Contains_DifferentAddressFamily_ReturnsFalse()
 
         [Theory]
         [InlineData("0.0.0.0/0", "0.0.0.0", "127.127.127.127", "255.255.255.255")] // the whole IPv4 space
+        [InlineData("0.0.0.0/0", "0.0.0.0", "::ffff:127.127.127.127", "::ffff:255.255.255.255")] // the whole IPv4 space
         [InlineData("::/0", "::", "ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff")] // the whole IPv6 space
         [InlineData("255.255.255.255/32", "255.255.255.255")] // single IPv4 address
         [InlineData("ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff/128", "ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff")] // single IPv6 address
         [InlineData("255.255.255.0/24", "255.255.255.0", "255.255.255.255")]
+        [InlineData("255.255.255.0/24", "::ffff:255.255.255.0", "::ffff:255.255.255.255")]
         [InlineData("198.51.248.0/22", "198.51.248.0", "198.51.250.42", "198.51.251.255")]
         [InlineData("255.255.255.128/25", "255.255.255.128", "255.255.255.129", "255.255.255.255")]
         [InlineData("2a00::/13", "2a00::", "2a00::1", "2a01::", "2a07::", "2a07:ffff:ffff:ffff:ffff:ffff:ffff:ffff")]