diff --git a/lib/logstash/inputs/imap.rb b/lib/logstash/inputs/imap.rb
index 6ff34e7..698ccdf 100644
--- a/lib/logstash/inputs/imap.rb
+++ b/lib/logstash/inputs/imap.rb
@@ -225,7 +225,7 @@ def parse_mail(mail)
 
     @codec.decode(message) do |event|
       # Use the 'Date' field as the timestamp
-      event.timestamp = LogStash::Timestamp.new(mail.date.to_time)
+      event.timestamp = LogStash::Timestamp.new(mail.date&.to_time)
 
       process_headers(mail, event) if @headers_target
 
diff --git a/spec/inputs/imap_spec.rb b/spec/inputs/imap_spec.rb
index 0d9c74b..fa74908 100644
--- a/spec/inputs/imap_spec.rb
+++ b/spec/inputs/imap_spec.rb
@@ -170,6 +170,18 @@
       end
     end
 
+    context "missing date" do
+      before do
+        mail.date = nil
+      end
+
+      it "should not cause an exception" do
+        event = input.parse_mail(mail)
+        expect( event.include?('Date') ).to be false
+        expect( event.timestamp ).not_to be nil
+      end
+    end
+
     context "headers_target => ''" do
       let(:config) { super().merge("headers_target" => '') }