diff --git a/SlackNet.Tests/UtilsTests.cs b/SlackNet.Tests/UtilsTests.cs
index 6135b3d..0e576b1 100644
--- a/SlackNet.Tests/UtilsTests.cs
+++ b/SlackNet.Tests/UtilsTests.cs
@@ -17,6 +17,52 @@ public void SetUp()
             _scheduler = new TestScheduler();
         }
 
+        [Test]
+        public void ToDateTime_FromTimestampString_NullOrEmpty_ReturnsNull()
+        {
+            ((string)null).ToDateTime().ShouldBeNull();
+            string.Empty.ToDateTime().ShouldBeNull();
+        }
+
+        [Test]
+        public void ToDateTime_FromTimestampString_InvalidTimestamp_ReturnsNull()
+        {
+            "foo".ToDateTime().ShouldBeNull();
+        }
+
+        [Test]
+        public void ToDateTime_FromTimestampString_ValidTimestamp_ReturnsDateTime()
+        {
+            "42".ToDateTime().ShouldBe(new DateTime(1970, 1, 1, 0, 0, 42));
+            "-42".ToDateTime().ShouldBe(new DateTime(1969, 12, 31, 23, 59, 18));
+        }
+
+        [Test]
+        public void ToDateTime_FromInteger_Zero_ReturnsNull()
+        {
+            0.ToDateTime().ShouldBeNull();
+        }
+
+        [Test]
+        public void ToDateTime_FromInteger_NonZero_ReturnsDateTime()
+        {
+            42.ToDateTime().ShouldBe(new DateTime(1970, 1, 1, 0, 0, 42));
+            (-42).ToDateTime().ShouldBe(new DateTime(1969, 12, 31, 23, 59, 18));
+        }
+
+        [Test]
+        public void ToDateTime_FromDecimal_Zero_ReturnsNull()
+        {
+            0m.ToDateTime().ShouldBeNull();
+        }
+
+        [Test]
+        public void ToDateTime_FromDecimal_NonZero_ReturnsDateTime()
+        {
+            42m.ToDateTime().ShouldBe(new DateTime(1970, 1, 1, 0, 0, 42));
+            (-42m).ToDateTime().ShouldBe(new DateTime(1969, 12, 31, 23, 59, 18));
+        }
+
         [Test]
         public void RetryWithDelay_NoError_PassesThrough()
         {
diff --git a/SlackNet/Utils.cs b/SlackNet/Utils.cs
index 41ad102..284ff6d 100644
--- a/SlackNet/Utils.cs
+++ b/SlackNet/Utils.cs
@@ -17,7 +17,9 @@ public static class Utils
         public static DateTime? ToDateTime(this string timestamp) =>
             string.IsNullOrEmpty(timestamp)
                 ? null
-                : Decimal.Parse(timestamp).ToDateTime();
+                : decimal.TryParse(timestamp, out var ts)
+                    ? ts.ToDateTime()
+                    : null;
 
         /// <summary>
         /// Converts a Slack timestamp number to a <see cref="DateTime"/>.
@@ -30,7 +32,7 @@ public static class Utils
         /// </summary>
         /// <returns>If timestamp is 0, returns null, otherwise a DateTime.</returns>
         public static DateTime? ToDateTime(this decimal timestamp) =>
-            timestamp == 0
+            timestamp != 0
                 ? DateTimeOffset.FromUnixTimeMilliseconds((long)(timestamp * 1000)).UtcDateTime
                 : (DateTime?)null;