diff --git a/MimeKit/AsyncMimeReader.cs b/MimeKit/AsyncMimeReader.cs
index 91e6b02c2e..3e484cfc88 100644
--- a/MimeKit/AsyncMimeReader.cs
+++ b/MimeKit/AsyncMimeReader.cs
@@ -178,7 +178,7 @@ async Task StepHeadersAsync (CancellationToken cancellationToken)
 							if (await ReadAheadAsync (atleast, 0, cancellationToken).ConfigureAwait (false) < atleast)
 								break;
 						} while (true);
-					} else if (input[inputIndex] == (byte) 'F') {
+					} else if (input[inputIndex] == (byte) 'F' || input[inputIndex] == (byte) '>') {
 						// Check for an mbox-style From-line. Again, if the message is properly formatted and not truncated, this will NEVER happen.
 						do {
 							unsafe {
diff --git a/UnitTests/ExperimentalMimeParserTests.cs b/UnitTests/ExperimentalMimeParserTests.cs
index 1f6c40ef2a..5e9cfca4c6 100644
--- a/UnitTests/ExperimentalMimeParserTests.cs
+++ b/UnitTests/ExperimentalMimeParserTests.cs
@@ -2571,6 +2571,80 @@ public async Task TestMimePartBasicAsync ()
 			}
 		}
 
+		[Test]
+		public void TestGarbageBeforeMessageHeaders ()
+		{
+			string text = @">F!&^#%&^
+From: mimekit@example.com
+To: mimekit@example.com
+Subject: This message has garbage before the headers
+Date: Tue, 12 Nov 2013 09:12:42 -0500
+MIME-Version: 1.0
+Content-Type: text/plain; charset=utf-8
+
+This is the message body.
+".Replace ("\r\n", "\n");
+
+			using (var stream = new MemoryStream (Encoding.ASCII.GetBytes (text), false)) {
+				var parser = new ExperimentalMimeParser (stream, MimeFormat.Entity);
+
+				Assert.Throws<FormatException> (() => parser.ParseMessage ());
+			}
+
+			using (var stream = new MemoryStream (Encoding.ASCII.GetBytes (text.Replace ("\n", "\r\n")), false)) {
+				var parser = new ExperimentalMimeParser (stream, MimeFormat.Entity);
+
+				Assert.Throws<FormatException> (() => parser.ParseMessage ());
+			}
+
+			using (var stream = new MemoryStream (Encoding.ASCII.GetBytes (text), false)) {
+				var parser = new ExperimentalMimeParser (stream, MimeFormat.Entity);
+
+				Assert.ThrowsAsync<FormatException> (async () => await parser.ParseMessageAsync ());
+			}
+
+			using (var stream = new MemoryStream (Encoding.ASCII.GetBytes (text.Replace ("\n", "\r\n")), false)) {
+				var parser = new ExperimentalMimeParser (stream, MimeFormat.Entity);
+
+				Assert.ThrowsAsync<FormatException> (async () => await parser.ParseMessageAsync ());
+			}
+		}
+
+		[Test]
+		public void TestGarbageBeforeEntityHeaders ()
+		{
+			string text = @">F!&^#%&^
+MIME-Version: 1.0
+Content-Type: text/plain; charset=utf-8
+
+This is the message body.
+".Replace ("\r\n", "\n");
+
+			using (var stream = new MemoryStream (Encoding.ASCII.GetBytes (text), false)) {
+				var parser = new ExperimentalMimeParser (stream, MimeFormat.Entity);
+
+				Assert.Throws<FormatException> (() => parser.ParseEntity ());
+			}
+
+			using (var stream = new MemoryStream (Encoding.ASCII.GetBytes (text.Replace ("\n", "\r\n")), false)) {
+				var parser = new ExperimentalMimeParser (stream, MimeFormat.Entity);
+
+				Assert.Throws<FormatException> (() => parser.ParseEntity ());
+			}
+
+			using (var stream = new MemoryStream (Encoding.ASCII.GetBytes (text), false)) {
+				var parser = new ExperimentalMimeParser (stream, MimeFormat.Entity);
+
+				Assert.ThrowsAsync<FormatException> (async () => await parser.ParseEntityAsync ());
+			}
+
+			using (var stream = new MemoryStream (Encoding.ASCII.GetBytes (text.Replace ("\n", "\r\n")), false)) {
+				var parser = new ExperimentalMimeParser (stream, MimeFormat.Entity);
+
+				Assert.ThrowsAsync<FormatException> (async () => await parser.ParseEntityAsync ());
+			}
+		}
+
 		static void AssertSimpleMbox (Stream stream)
 		{
 			var parser = new ExperimentalMimeParser (stream, MimeFormat.Mbox);
diff --git a/UnitTests/MimeParserTests.cs b/UnitTests/MimeParserTests.cs
index 4d8c007b28..f72ef1ea9e 100644
--- a/UnitTests/MimeParserTests.cs
+++ b/UnitTests/MimeParserTests.cs
@@ -2555,6 +2555,80 @@ public async Task TestMimePartBasicAsync ()
 			}
 		}
 
+		[Test]
+		public void TestGarbageBeforeMessageHeaders ()
+		{
+			string text = @">F!&^#%&^
+From: mimekit@example.com
+To: mimekit@example.com
+Subject: This message has garbage before the headers
+Date: Tue, 12 Nov 2013 09:12:42 -0500
+MIME-Version: 1.0
+Content-Type: text/plain; charset=utf-8
+
+This is the message body.
+".Replace ("\r\n", "\n");
+
+			using (var stream = new MemoryStream (Encoding.ASCII.GetBytes (text), false)) {
+				var parser = new MimeParser (stream, MimeFormat.Entity);
+
+				Assert.Throws<FormatException> (() => parser.ParseMessage ());
+			}
+
+			using (var stream = new MemoryStream (Encoding.ASCII.GetBytes (text.Replace ("\n", "\r\n")), false)) {
+				var parser = new MimeParser (stream, MimeFormat.Entity);
+
+				Assert.Throws<FormatException> (() => parser.ParseMessage ());
+			}
+
+			using (var stream = new MemoryStream (Encoding.ASCII.GetBytes (text), false)) {
+				var parser = new MimeParser (stream, MimeFormat.Entity);
+
+				Assert.ThrowsAsync<FormatException> (async () => await parser.ParseMessageAsync ());
+			}
+
+			using (var stream = new MemoryStream (Encoding.ASCII.GetBytes (text.Replace ("\n", "\r\n")), false)) {
+				var parser = new MimeParser (stream, MimeFormat.Entity);
+
+				Assert.ThrowsAsync<FormatException> (async () => await parser.ParseMessageAsync ());
+			}
+		}
+
+		[Test]
+		public void TestGarbageBeforeEntityHeaders ()
+		{
+			string text = @">F!&^#%&^
+MIME-Version: 1.0
+Content-Type: text/plain; charset=utf-8
+
+This is the message body.
+".Replace ("\r\n", "\n");
+
+			using (var stream = new MemoryStream (Encoding.ASCII.GetBytes (text), false)) {
+				var parser = new MimeParser (stream, MimeFormat.Entity);
+
+				Assert.Throws<FormatException> (() => parser.ParseEntity ());
+			}
+
+			using (var stream = new MemoryStream (Encoding.ASCII.GetBytes (text.Replace ("\n", "\r\n")), false)) {
+				var parser = new MimeParser (stream, MimeFormat.Entity);
+
+				Assert.Throws<FormatException> (() => parser.ParseEntity ());
+			}
+
+			using (var stream = new MemoryStream (Encoding.ASCII.GetBytes (text), false)) {
+				var parser = new MimeParser (stream, MimeFormat.Entity);
+
+				Assert.ThrowsAsync<FormatException> (async () => await parser.ParseEntityAsync ());
+			}
+
+			using (var stream = new MemoryStream (Encoding.ASCII.GetBytes (text.Replace ("\n", "\r\n")), false)) {
+				var parser = new MimeParser (stream, MimeFormat.Entity);
+
+				Assert.ThrowsAsync<FormatException> (async () => await parser.ParseEntityAsync ());
+			}
+		}
+
 		static void AssertSimpleMbox (Stream stream)
 		{
 			var parser = new MimeParser (stream, MimeFormat.Mbox);