diff --git a/src/ModelContextProtocol.Core/Protocol/ContentBlock.cs b/src/ModelContextProtocol.Core/Protocol/ContentBlock.cs
index d31936b..7d35cec 100644
--- a/src/ModelContextProtocol.Core/Protocol/ContentBlock.cs
+++ b/src/ModelContextProtocol.Core/Protocol/ContentBlock.cs
@@ -425,9 +425,12 @@ public sealed class ImageContentBlock : ContentBlock
     /// <remarks>
     /// This method stores the provided bytes as <see cref="DecodedData"/> and encodes them to base64 UTF-8 bytes for <see cref="Data"/>.
     /// </remarks>
-    /// <exception cref="InvalidOperationException"></exception>
+    /// <exception cref="ArgumentNullException"><paramref name="mimeType"/> is <see langword="null"/>.</exception>
+    /// <exception cref="ArgumentException"><paramref name="mimeType"/> is empty or composed entirely of whitespace.</exception>
     public static ImageContentBlock FromBytes(ReadOnlyMemory<byte> bytes, string mimeType)
     {
+        Throw.IfNullOrWhiteSpace(mimeType);
+
         ReadOnlyMemory<byte> data = EncodingUtilities.EncodeToBase64Utf8(bytes);
         
         return new()
@@ -510,9 +513,12 @@ public sealed class AudioContentBlock : ContentBlock
     /// <remarks>
     /// This method stores the provided bytes as <see cref="DecodedData"/> and encodes them to base64 UTF-8 bytes for <see cref="Data"/>.
     /// </remarks>
-    /// <exception cref="InvalidOperationException"></exception>
+    /// <exception cref="ArgumentNullException"><paramref name="mimeType"/> is <see langword="null"/>.</exception>
+    /// <exception cref="ArgumentException"><paramref name="mimeType"/> is empty or composed entirely of whitespace.</exception>
     public static AudioContentBlock FromBytes(ReadOnlyMemory<byte> bytes, string mimeType)
     {
+        Throw.IfNullOrWhiteSpace(mimeType);
+
         ReadOnlyMemory<byte> data = EncodingUtilities.EncodeToBase64Utf8(bytes);
         
         return new()
diff --git a/tests/ModelContextProtocol.Tests/Protocol/ContentBlockTests.cs b/tests/ModelContextProtocol.Tests/Protocol/ContentBlockTests.cs
index 2dfcf7d..957a452 100644
--- a/tests/ModelContextProtocol.Tests/Protocol/ContentBlockTests.cs
+++ b/tests/ModelContextProtocol.Tests/Protocol/ContentBlockTests.cs
@@ -272,4 +272,22 @@ public class ContentBlockTests
         Assert.Equal("Paris", result.Input.GetProperty("city").GetString());
         Assert.Equal("metric", result.Input.GetProperty("units").GetString());
     }
+
+    [Theory]
+    [InlineData(null)]
+    [InlineData("")]
+    [InlineData(" ")]
+    public void ImageContentBlock_FromBytes_ThrowsForNullOrWhiteSpaceMimeType(string? mimeType)
+    {
+        Assert.ThrowsAny<ArgumentException>(() => ImageContentBlock.FromBytes((byte[])[1, 2, 3], mimeType!));
+    }
+
+    [Theory]
+    [InlineData(null)]
+    [InlineData("")]
+    [InlineData(" ")]
+    public void AudioContentBlock_FromBytes_ThrowsForNullOrWhiteSpaceMimeType(string? mimeType)
+    {
+        Assert.ThrowsAny<ArgumentException>(() => AudioContentBlock.FromBytes((byte[])[1, 2, 3], mimeType!));
+    }
 }
\ No newline at end of file