diff --git a/cs/config/Make.rules.mak.cs b/cs/config/Make.rules.mak.cs
index 5501714..197af28 100644
--- a/cs/config/Make.rules.mak.cs
+++ b/cs/config/Make.rules.mak.cs
@@ -183,7 +183,7 @@ MCSFLAGS 		= $(MCSFLAGS) -optimize+
 #MCSFLAGS		= $(MCSFLAGS) -define:CODE_ANALYSIS
 
 !if "$(FRAMEWORK)" == "3.5"
-MCSFLAGS = $(MCSFLAGS) /noconfig /nostdlib+ 
+MCSFLAGS = $(MCSFLAGS) /noconfig /nostdlib+ /define:DOTNET3_5
 MCSFLAGS = $(MCSFLAGS) /reference:"$(FRAMEWORKDIR)\v2.0.50727\mscorlib.dll"
 MCSFLAGS = $(MCSFLAGS) /reference:"$(FRAMEWORKDIR)\v2.0.50727\System.dll"
 MCSFLAGS = $(MCSFLAGS) /reference:"$(FRAMEWORKDIR)\v2.0.50727\System.Data.dll"
diff --git a/cs/src/Ice/Network.cs b/cs/src/Ice/Network.cs
index b2fa6cc..0b080e2 100644
--- a/cs/src/Ice/Network.cs
+++ b/cs/src/Ice/Network.cs
@@ -459,7 +459,10 @@ namespace IceInternal
         public static Socket createServerSocket(bool udp, AddressFamily family, int protocol)
         {
             Socket socket = createSocket(udp, family);
-#  if !COMPACT && !UNITY && !__MonoCS__ && !SILVERLIGHT
+#  if !COMPACT && !UNITY && !__MonoCS__ && !SILVERLIGHT && !DOTNET3_5
+            //
+            // The IPv6Only enumerator was added in .NET 4.
+            //
             if(family == AddressFamily.InterNetworkV6 && protocol != EnableIPv4)
             {
                 try
diff --git a/cs/test/Ice/binding/AllTests.cs b/cs/test/Ice/binding/AllTests.cs
index 92f29fa..d378ea8 100644
--- a/cs/test/Ice/binding/AllTests.cs
+++ b/cs/test/Ice/binding/AllTests.cs
@@ -850,7 +850,7 @@ public class AllTests : TestCommon.TestApp
             WriteLine("ok");
         }
 
-#if !SILVERLIGHT && !COMPACT && !UNITY
+#if !SILVERLIGHT && !COMPACT && !UNITY && !DOTNET3_5
         {
             Write("testing ipv4 & ipv6 connections... ");
             Flush();