diff --git a/codec-smtp/src/main/java/io/netty/handler/codec/smtp/SmtpResponseDecoder.java b/codec-smtp/src/main/java/io/netty/handler/codec/smtp/SmtpResponseDecoder.java
index 13587b36bc..eadea32654 100644
--- a/codec-smtp/src/main/java/io/netty/handler/codec/smtp/SmtpResponseDecoder.java
+++ b/codec-smtp/src/main/java/io/netty/handler/codec/smtp/SmtpResponseDecoder.java
@@ -69,7 +69,11 @@ public final class SmtpResponseDecoder extends LineBasedFrameDecoder {
                         details.add(detail);
                     }
                 } else {
-                    details = Collections.singletonList(detail);
+                    if (detail == null) {
+                        details = Collections.emptyList();
+                    } else {
+                        details = Collections.singletonList(detail);
+                    }
                 }
                 return new DefaultSmtpResponse(code, details);
             case '-':
diff --git a/codec-smtp/src/test/java/io/netty/handler/codec/smtp/SmtpResponseDecoderTest.java b/codec-smtp/src/test/java/io/netty/handler/codec/smtp/SmtpResponseDecoderTest.java
index 7ccc993acb..24044fa287 100644
--- a/codec-smtp/src/test/java/io/netty/handler/codec/smtp/SmtpResponseDecoderTest.java
+++ b/codec-smtp/src/test/java/io/netty/handler/codec/smtp/SmtpResponseDecoderTest.java
@@ -43,6 +43,18 @@ public class SmtpResponseDecoderTest {
         assertNull(channel.readInbound());
     }
 
+    @Test
+    public void testDecodeOneLineResponseNoDetails() {
+        EmbeddedChannel channel = newChannel();
+        assertTrue(channel.writeInbound(newBuffer("250 \r\n")));
+        assertTrue(channel.finish());
+
+        SmtpResponse response = channel.readInbound();
+        assertEquals(250, response.code());
+        List<CharSequence> sequences = response.details();
+        assertEquals(0, sequences.size());
+    }
+
     @Test
     public void testDecodeOneLineResponseChunked() {
         EmbeddedChannel channel = newChannel();