diff --git a/MoreLinq.Test/MoreLinq.Test.csproj b/MoreLinq.Test/MoreLinq.Test.csproj
index 198a6756e..32d7ac7b7 100644
--- a/MoreLinq.Test/MoreLinq.Test.csproj
+++ b/MoreLinq.Test/MoreLinq.Test.csproj
@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <AssemblyTitle>MoreLinq.Test</AssemblyTitle>
-    <TargetFrameworks>net7.0;net6.0;netcoreapp3.1;net462</TargetFrameworks>
+    <TargetFrameworks>net7.0;net6.0;net462</TargetFrameworks>
     <DebugType>portable</DebugType>
     <AssemblyName>MoreLinq.Test</AssemblyName>
     <OutputType Condition="'$(TargetFramework)' == 'net462'">Exe</OutputType>
diff --git a/MoreLinq.Test/NullArgumentTest.cs b/MoreLinq.Test/NullArgumentTest.cs
index d17e2372a..9cd3ec8cd 100644
--- a/MoreLinq.Test/NullArgumentTest.cs
+++ b/MoreLinq.Test/NullArgumentTest.cs
@@ -57,12 +57,6 @@ static IEnumerable<ITestCaseData> GetNotNullTestCases() =>
                 Debug.Assert(e is not null);
                 var stackTrace = new StackTrace(e, false);
                 var stackFrame = stackTrace.GetFrames().First();
-#if NETCOREAPP3_1
-                // Under .NET Core 3.1, "StackTrace.GetFrames()" was defined to return an array
-                // of nullable frame elements. See:
-                // https://github.com/dotnet/corefx/blob/v3.1.32/src/Common/src/CoreLib/System/Diagnostics/StackTrace.cs#L162
-                Debug.Assert(stackFrame is not null);
-#endif
                 var actualType = stackFrame.GetMethod()?.DeclaringType;
                 Assert.That(actualType, Is.SameAs(typeof(MoreEnumerable)));
             });
diff --git a/appveyor.yml b/appveyor.yml
index efb73541b..0ac9ab5a6 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -53,10 +53,8 @@ install:
 - eclint check -w "**/*.{cs,tt,cmd,sh,md,txt,yml,json,sln,csproj,shfbproj}"
 - git reset --hard
 - ps: if ($isWindows) { tools\dotnet-install.ps1 -JSonFile global.json }
-- ps: if ($isWindows) { tools\dotnet-install.ps1 -Runtime dotnet -Version 3.1.10 -SkipNonVersionedFiles }
 - ps: if ($isWindows) { tools\dotnet-install.ps1 -Runtime dotnet -Version 6.0.11 -SkipNonVersionedFiles }
 - sh: ./tools/dotnet-install.sh --jsonfile global.json
-- sh: ./tools/dotnet-install.sh --runtime dotnet --version 3.1.10 --skip-non-versioned-files
 - sh: ./tools/dotnet-install.sh --runtime dotnet --version 6.0.11 --skip-non-versioned-files
 - sh: export PATH="$HOME/.dotnet:$PATH"
 before_build:
diff --git a/test.cmd b/test.cmd
index 7f87f56c0..eec32dd03 100644
--- a/test.cmd
+++ b/test.cmd
@@ -12,8 +12,6 @@ call build ^
   && call :test net7.0 Release ^
   && call :test net6.0 Debug ^
   && call :test net6.0 Release ^
-  && call :test netcoreapp3.1 Debug ^
-  && call :test netcoreapp3.1 Release ^
   && call :test net462 Debug ^
   && call :test net462 Release ^
   && call :report-cover
diff --git a/test.sh b/test.sh
index c228eabe2..90d26eff9 100755
--- a/test.sh
+++ b/test.sh
@@ -10,7 +10,7 @@ if [[ -z "$1" ]]; then
 else
     configs="$1"
 fi
-for f in netcoreapp3.1 net6.0 net7.0; do
+for f in net6.0 net7.0; do
     for c in $configs; do
         dotnet test --no-build -c $c -f $f --settings MoreLinq.Test/coverlet.runsettings MoreLinq.Test
         TEST_RESULTS_DIR="$(ls -dc MoreLinq.Test/TestResults/* | head -1)"