diff --git a/PolyShim.Tests/Net100/TimeSpanTests.cs b/PolyShim.Tests/Net100/TimeSpanTests.cs
new file mode 100644
index 0000000..55b1e02
--- /dev/null
+++ b/PolyShim.Tests/Net100/TimeSpanTests.cs
@@ -0,0 +1,17 @@
+using System;
+using FluentAssertions;
+using Xunit;
+
+namespace PolyShim.Tests.Net100;
+
+public class TimeSpanTests
+{
+    [Fact]
+    public void FromMilliseconds_Test()
+    {
+        // Act & assert
+        TimeSpan.FromMilliseconds(1234).Should().Be(TimeSpan.FromSeconds(1.234));
+        TimeSpan.FromMilliseconds(0).Should().Be(TimeSpan.Zero);
+        TimeSpan.FromMilliseconds(-1000).Should().Be(TimeSpan.FromSeconds(-1));
+    }
+}
diff --git a/PolyShim.Tests/Net90/TimeSpanTests.cs b/PolyShim.Tests/Net90/TimeSpanTests.cs
new file mode 100644
index 0000000..3fe8413
--- /dev/null
+++ b/PolyShim.Tests/Net90/TimeSpanTests.cs
@@ -0,0 +1,17 @@
+using System;
+using FluentAssertions;
+using Xunit;
+
+namespace PolyShim.Tests.Net90;
+
+public class TimeSpanTests
+{
+    [Fact]
+    public void FromMilliseconds_Test()
+    {
+        // Act & assert
+        TimeSpan.FromMilliseconds(1234, 567).Should().Be(TimeSpan.FromSeconds(1.234567));
+        TimeSpan.FromMilliseconds(0, 0).Should().Be(TimeSpan.Zero);
+        TimeSpan.FromMilliseconds(-1000, -500).Should().Be(TimeSpan.FromSeconds(-1.0005));
+    }
+}
diff --git a/PolyShim/Net100/TimeSpan.cs b/PolyShim/Net100/TimeSpan.cs
new file mode 100644
index 0000000..47d755f
--- /dev/null
+++ b/PolyShim/Net100/TimeSpan.cs
@@ -0,0 +1,19 @@
+#if (NETCOREAPP && !NET10_0_OR_GREATER) || (NETFRAMEWORK) || (NETSTANDARD)
+#nullable enable
+// ReSharper disable RedundantUsingDirective
+// ReSharper disable CheckNamespace
+// ReSharper disable InconsistentNaming
+// ReSharper disable PartialTypeWithSinglePart
+
+using System;
+
+internal static partial class PolyfillExtensions
+{
+    extension(TimeSpan)
+    {
+        // https://learn.microsoft.com/dotnet/api/system.timespan.frommilliseconds#system-timespan-frommilliseconds(system-int64)
+        public static TimeSpan FromMilliseconds(long milliseconds) =>
+            TimeSpan.FromMilliseconds(milliseconds, 0);
+    }
+}
+#endif
diff --git a/PolyShim/Net90/TimeSpan.cs b/PolyShim/Net90/TimeSpan.cs
new file mode 100644
index 0000000..3f77cf1
--- /dev/null
+++ b/PolyShim/Net90/TimeSpan.cs
@@ -0,0 +1,19 @@
+#if (NETCOREAPP && !NET9_0_OR_GREATER) || (NETFRAMEWORK) || (NETSTANDARD)
+#nullable enable
+// ReSharper disable RedundantUsingDirective
+// ReSharper disable CheckNamespace
+// ReSharper disable InconsistentNaming
+// ReSharper disable PartialTypeWithSinglePart
+
+using System;
+
+internal static partial class PolyfillExtensions
+{
+    extension(TimeSpan)
+    {
+        // https://learn.microsoft.com/dotnet/api/system.timespan.frommilliseconds#system-timespan-frommilliseconds(system-int64-system-int64)
+        public static TimeSpan FromMilliseconds(long milliseconds, long microseconds) =>
+            TimeSpan.FromMilliseconds(milliseconds + microseconds / 1_000.0);
+    }
+}
+#endif