diff --git a/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.Sdk.BeforeCommon.targets b/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.Sdk.BeforeCommon.targets
index 8b42b2d6e847..c3f08df257a4 100644
--- a/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.Sdk.BeforeCommon.targets
+++ b/src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.Sdk.BeforeCommon.targets
@@ -206,10 +206,19 @@ Copyright (c) .NET Foundation. All rights reserved.
     </ItemGroup>
   </Target>
 
+  <!-- Add conditional compilation symbols for target platform backwards compatibility. -->
+  <Target Name="GeneratePlatformCompatibleDefineConstants"
+          Condition=" '$(DisableImplicitFrameworkDefines)' != 'true' and '$(TargetPlatformIdentifier)' != '' and '$(TargetFrameworkIdentifier)' == '.NETCoreApp' and $([MSBuild]::VersionGreaterThanOrEquals($(TargetFrameworkVersion), 5.0)) " >
+    <ItemGroup>
+      <_SupportedPlatformCompatibleVersions Include="@(SupportedTargetPlatform)" Condition=" %(Identity) != '' and $([MSBuild]::VersionLessThan(%(Identity), $(TargetPlatformVersion))) " />
+      <_ImplicitDefineConstant Include="@(_SupportedPlatformCompatibleVersions->'$(TargetPlatformIdentifier.ToUpper())%(Identity)'->Replace('.', '_'))" />
+    </ItemGroup>
+  </Target>
+
   <!-- Add implicitly defined preprocessor symbols to DefineConstants -->
   <Target Name="AddImplicitDefineConstants"
           Condition=" '$(DisableImplicitFrameworkDefines)' != 'true' "
-          DependsOnTargets="GenerateTargetPlatformDefineConstants;GenerateNETCompatibleDefineConstants"
+          DependsOnTargets="GenerateTargetPlatformDefineConstants;GenerateNETCompatibleDefineConstants;GeneratePlatformCompatibleDefineConstants"
           BeforeTargets="CoreCompile" >
     <PropertyGroup>
       <DefineConstants Condition=" '@(_ImplicitDefineConstant)' != '' " >$(DefineConstants);@(_ImplicitDefineConstant)</DefineConstants>
diff --git a/src/Tests/Microsoft.NET.Build.Tests/GivenThatWeWantToBuildALibrary.cs b/src/Tests/Microsoft.NET.Build.Tests/GivenThatWeWantToBuildALibrary.cs
index ef98b64c861d..01a79dc6de4d 100644
--- a/src/Tests/Microsoft.NET.Build.Tests/GivenThatWeWantToBuildALibrary.cs
+++ b/src/Tests/Microsoft.NET.Build.Tests/GivenThatWeWantToBuildALibrary.cs
@@ -447,6 +447,42 @@ public void It_implicitly_defines_compilation_constants_for_the_target_platform(
             AssertDefinedConstantsOutput(testAsset, targetFramework, new[] { "NETCOREAPP", "NET", "NET5_0", "NETCOREAPP3_1" }.Concat(expectedDefines).ToArray());
         }
 
+        [Theory]
+        [InlineData(new[] { "1.0", "1.1" }, "ios", "1.1", new[] { "IOS", "IOS1_1", "IOS1_0" })]
+        [InlineData(new[] { "11.11", "12.12", "13.13" }, "android", "12.12", new[] { "ANDROID", "ANDROID11_11", "ANDROID12_12" })]
+        [InlineData(new[] { "7.0", "8.0", "10.0.19041", "11.0.0" }, "windows", "11.0.0", new[] { "WINDOWS", "WINDOWS7_0", "WINDOWS8_0", "WINDOWS10_0_19041", "WINDOWS11_0_0" })]
+        public void It_implicitly_defines_compilation_constants_for_the_target_platform_with_backwards_compatibility(string[] supportedTargetPlatform, string targetPlatformIdentifier, string targetPlatformVersion, string[] expectedDefines)
+        {
+            var targetFramework = "net5.0";
+            var testAsset = _testAssetsManager
+                .CopyTestAsset("AppWithLibrary", "ImplicitFrameworkConstants", targetFramework)
+                .WithSource()
+                .WithTargetFramework(targetFramework)
+                .WithProjectChanges(project =>
+                {
+                    //  Manually set target plaform properties
+                    var ns = project.Root.Name.Namespace;
+                    var propGroup = new XElement(ns + "PropertyGroup");
+                    project.Root.Add(propGroup);
+
+                    var platformIdentifier = new XElement(ns + "TargetPlatformIdentifier", targetPlatformIdentifier);
+                    propGroup.Add(platformIdentifier);
+                    var platformVersion = new XElement(ns + "TargetPlatformVersion", targetPlatformVersion);
+                    propGroup.Add(platformVersion);
+                    var disableUnnecessaryImplicitFrameworkReferencesForThisTest = new XElement(ns + "DisableImplicitFrameworkReferences", "true");
+                    propGroup.Add(disableUnnecessaryImplicitFrameworkReferencesForThisTest);
+
+                    var itemGroup = new XElement(ns + "ItemGroup");
+                    project.Root.Add(itemGroup);
+                    foreach (var targetPlatform in supportedTargetPlatform)
+                    {
+                        itemGroup.Add(new XElement(ns + "SupportedTargetPlatform", new XAttribute("Include", targetPlatform)));
+                    }
+                });
+
+            AssertDefinedConstantsOutput(testAsset, targetFramework, new[] { "NETCOREAPP", "NET", "NET5_0", "NETCOREAPP3_1" }.Concat(expectedDefines).ToArray());
+        }
+
         private void AssertDefinedConstantsOutput(TestAsset testAsset, string targetFramework, string[] expectedDefines)
         {
             var libraryProjectDirectory = Path.Combine(testAsset.TestRoot, "TestLibrary");
@@ -468,6 +504,71 @@ private void AssertDefinedConstantsOutput(TestAsset testAsset, string targetFram
             definedConstants.Should().BeEquivalentTo(new[] { "DEBUG", "TRACE" }.Concat(expectedDefines).ToArray());
         }
 
+        [WindowsOnlyTheory]
+        [InlineData("netcoreapp3.1", new[] { "NETCOREAPP", "NETCOREAPP3_1" })]
+        [InlineData("net5.0", new[] { "NETCOREAPP", "NETCOREAPP3_1", "NET", "NET5_0", "WINDOWS", "WINDOWS7_0" }, "windows", "7.0")]
+        public void It_can_use_implicitly_defined_compilation_constants(string targetFramework, string[] expectedOutput, string targetPlatformIdentifier = null, string targetPlatformVersion = null)
+        {
+            var testProj = new TestProject()
+            {
+                Name = "CompilationConstants",
+                TargetFrameworks = targetFramework,
+                IsExe = true,
+                IsSdkProject = true
+            };
+            if (targetPlatformIdentifier != null)
+            {
+                testProj.AdditionalProperties["TargetPlatformIdentifier"] = targetPlatformIdentifier;
+                testProj.AdditionalProperties["TargetPlatformVersion"] = targetPlatformVersion;
+            }
+            var testAsset = _testAssetsManager.CreateTestProject(testProj);
+            File.WriteAllText(Path.Combine(testAsset.Path, testProj.Name, $"{testProj.Name}.cs"), @"
+using System;
+class Program
+{
+    static void Main(string[] args)
+    {
+        #if NETCOREAPP
+            Console.WriteLine(""NETCOREAPP"");
+        #endif
+        #if NETCOREAPP2_1
+            Console.WriteLine(""NETCOREAPP2_1"");
+        #endif
+        #if NETCOREAPP3_1
+            Console.WriteLine(""NETCOREAPP3_1"");
+        #endif
+        #if NET
+            Console.WriteLine(""NET"");
+        #endif
+        #if NET5_0
+            Console.WriteLine(""NET5_0"");
+        #endif
+        #if WINDOWS
+            Console.WriteLine(""WINDOWS"");
+        #endif
+        #if WINDOWS7_0
+            Console.WriteLine(""WINDOWS7_0"");
+        #endif
+        #if IOS
+            Console.WriteLine(""IOS"");
+        #endif
+        #if IOS7_0
+            Console.WriteLine(""IOS7_0"");
+        #endif
+    }
+}");
+
+            var buildCommand = new BuildCommand(Log, Path.Combine(testAsset.Path, testProj.Name));
+            buildCommand
+                .Execute()
+                .Should()
+                .Pass();
+
+            var runCommand = new RunExeCommand(Log, Path.Combine(buildCommand.GetOutputDirectory(targetFramework).FullName, $"{testProj.Name}.exe"));
+            var stdOut = runCommand.Execute().StdOut.Split(Environment.NewLine.ToCharArray()).Where(line => !string.IsNullOrWhiteSpace(line));
+            stdOut.Should().BeEquivalentTo(expectedOutput);
+        }
+
         [Theory]
         [InlineData(false)]
         [InlineData(true)]