diff --git a/MailKit/Net/Imap/ImapFolderFetch.cs b/MailKit/Net/Imap/ImapFolderFetch.cs
index acaa4a4f7e..b9e593e238 100644
--- a/MailKit/Net/Imap/ImapFolderFetch.cs
+++ b/MailKit/Net/Imap/ImapFolderFetch.cs
@@ -443,28 +443,32 @@ string FormatSummaryItems (ref MessageSummaryItems items, HashSet<string> fields
 			}
 
 			if ((items & MessageSummaryItems.References) != 0 || fields != null) {
-				var headers = new StringBuilder ("BODY.PEEK[HEADER.FIELDS (");
-				bool references = false;
+				if (fields?.Count == 0)
+					tokens.Add ("BODY.PEEK[HEADER]");
+				else {
+					var headers = new StringBuilder ("BODY.PEEK[HEADER.FIELDS (");
+					bool references = false;
 
-				if (fields != null) {
-					foreach (var field in fields) {
-						var name = field.ToUpperInvariant ();
+					if (fields != null) {
+						foreach (var field in fields) {
+							var name = field.ToUpperInvariant ();
 
-						if (name == "REFERENCES")
-							references = true;
+							if (name == "REFERENCES")
+								references = true;
 
-						headers.Append (name);
-						headers.Append (' ');
+							headers.Append (name);
+							headers.Append (' ');
+						}
 					}
-				}
 
-				if ((items & MessageSummaryItems.References) != 0 && !references)
-					headers.Append ("REFERENCES ");
+ 					if ((items & MessageSummaryItems.References) != 0 && !references)
+						headers.Append ("REFERENCES ");
 
-				headers[headers.Length - 1] = ')';
-				headers.Append (']');
+					headers[headers.Length - 1] = ')';
+					headers.Append (']');
 
-				tokens.Add (headers.ToString ());
+					tokens.Add (headers.ToString ());
+				}
 			}
 
 			if (tokens.Count == 1)
@@ -672,8 +676,6 @@ async Task<IList<IMessageSummary>> FetchAsync (IList<UniqueId> uids, MessageSumm
 			if (fields == null)
 				throw new ArgumentNullException (nameof (fields));
 
-			if (fields.Count == 0)
-				throw new ArgumentException ("The set of header fields cannot be empty.", nameof (fields));
 
 			CheckState (true, false);