diff --git a/CHANGES b/CHANGES
index 79389eeefd..40ad8856b7 100644
--- a/CHANGES
+++ b/CHANGES
@@ -4,6 +4,9 @@ jsoup changelog
  * Improved startup time, particularly on Android, by reducing garbage generation and CPU execution time when loading
    the HTML entity files. About 1.72x faster in this area.
 
+ * Bugfix - a "SYSTEM" flag in doctype tags would be incorrectly removed.
+   <https://github.com/jhy/jsoup/issues/408>
+
 *** Release 1.10.1 [2016-Oct-23]
  * New feature: added the option to preserve case for tags and/or attributes, with ParseSettings. By default, the HTML
    parser will continue to normalize tag names and attribute names to lower case, and the XML parser will now preserve
diff --git a/src/main/java/org/jsoup/nodes/DocumentType.java b/src/main/java/org/jsoup/nodes/DocumentType.java
index 838ec6f720..4e7730b128 100644
--- a/src/main/java/org/jsoup/nodes/DocumentType.java
+++ b/src/main/java/org/jsoup/nodes/DocumentType.java
@@ -9,7 +9,10 @@
  * A {@code <!DOCTYPE>} node.
  */
 public class DocumentType extends Node {
+    public static final String PUBLIC_KEY = "PUBLIC";
+    public static final String SYSTEM_KEY = "SYSTEM";
     private static final String NAME = "name";
+    private static final String PUB_SYS_KEY = "pubSysKey"; // PUBLIC or SYSTEM
     private static final String PUBLIC_ID = "publicId";
     private static final String SYSTEM_ID = "systemId";
     // todo: quirk mode from publicId and systemId
@@ -26,6 +29,27 @@ public DocumentType(String name, String publicId, String systemId, String baseUr
 
         attr(NAME, name);
         attr(PUBLIC_ID, publicId);
+        if (has(PUBLIC_ID)) {
+            attr(PUB_SYS_KEY, PUBLIC_KEY);
+        }
+        attr(SYSTEM_ID, systemId);
+    }
+
+    /**
+     * Create a new doctype element.
+     * @param name the doctype's name
+     * @param publicId the doctype's public ID
+     * @param systemId the doctype's system ID
+     * @param baseUri the doctype's base URI
+     */
+    public DocumentType(String name, String pubSysKey, String publicId, String systemId, String baseUri) {
+        super(baseUri);
+
+        attr(NAME, name);
+        if (pubSysKey != null) {
+            attr(PUB_SYS_KEY, pubSysKey);
+        }
+        attr(PUBLIC_ID, publicId);
         attr(SYSTEM_ID, systemId);
     }
 
@@ -44,8 +68,10 @@ void outerHtmlHead(Appendable accum, int depth, Document.OutputSettings out) thr
         }
         if (has(NAME))
             accum.append(" ").append(attr(NAME));
+        if (has(PUB_SYS_KEY))
+            accum.append(" ").append(attr(PUB_SYS_KEY));
         if (has(PUBLIC_ID))
-            accum.append(" PUBLIC \"").append(attr(PUBLIC_ID)).append('"');
+            accum.append(" \"").append(attr(PUBLIC_ID)).append('"');
         if (has(SYSTEM_ID))
             accum.append(" \"").append(attr(SYSTEM_ID)).append('"');
         accum.append('>');
diff --git a/src/main/java/org/jsoup/parser/HtmlTreeBuilderState.java b/src/main/java/org/jsoup/parser/HtmlTreeBuilderState.java
index 9a4081405a..c515462c77 100644
--- a/src/main/java/org/jsoup/parser/HtmlTreeBuilderState.java
+++ b/src/main/java/org/jsoup/parser/HtmlTreeBuilderState.java
@@ -20,7 +20,7 @@ boolean process(Token t, HtmlTreeBuilder tb) {
                 // todo: quirk state check on doctype ids
                 Token.Doctype d = t.asDoctype();
                 DocumentType doctype = new DocumentType(
-                    tb.settings.normalizeTag(d.getName()), d.getPublicIdentifier(), d.getSystemIdentifier(), tb.getBaseUri());
+                    tb.settings.normalizeTag(d.getName()), d.getPubSysKey(), d.getPublicIdentifier(), d.getSystemIdentifier(), tb.getBaseUri());
                 tb.getDocument().appendChild(doctype);
                 if (d.isForceQuirks())
                     tb.getDocument().quirksMode(Document.QuirksMode.quirks);
diff --git a/src/main/java/org/jsoup/parser/Token.java b/src/main/java/org/jsoup/parser/Token.java
index 3b110c9125..34baf19699 100644
--- a/src/main/java/org/jsoup/parser/Token.java
+++ b/src/main/java/org/jsoup/parser/Token.java
@@ -32,6 +32,7 @@ static void reset(StringBuilder sb) {
 
     static final class Doctype extends Token {
         final StringBuilder name = new StringBuilder();
+        String pubSysKey = null;
         final StringBuilder publicIdentifier = new StringBuilder();
         final StringBuilder systemIdentifier = new StringBuilder();
         boolean forceQuirks = false;
@@ -43,6 +44,7 @@ static final class Doctype extends Token {
         @Override
         Token reset() {
             reset(name);
+            pubSysKey = null;
             reset(publicIdentifier);
             reset(systemIdentifier);
             forceQuirks = false;
@@ -53,6 +55,10 @@ String getName() {
             return name.toString();
         }
 
+        String getPubSysKey() {
+            return pubSysKey;
+        }
+
         String getPublicIdentifier() {
             return publicIdentifier.toString();
         }
diff --git a/src/main/java/org/jsoup/parser/TokeniserState.java b/src/main/java/org/jsoup/parser/TokeniserState.java
index 2e998d5219..6a97238d49 100644
--- a/src/main/java/org/jsoup/parser/TokeniserState.java
+++ b/src/main/java/org/jsoup/parser/TokeniserState.java
@@ -1,5 +1,7 @@
 package org.jsoup.parser;
 
+import org.jsoup.nodes.DocumentType;
+
 import java.util.Arrays;
 
 /**
@@ -1189,9 +1191,11 @@ void read(Tokeniser t, CharacterReader r) {
             else if (r.matches('>')) {
                 t.emitDoctypePending();
                 t.advanceTransition(Data);
-            } else if (r.matchConsumeIgnoreCase("PUBLIC")) {
+            } else if (r.matchConsumeIgnoreCase(DocumentType.PUBLIC_KEY)) {
+                t.doctypePending.pubSysKey = DocumentType.PUBLIC_KEY;
                 t.transition(AfterDoctypePublicKeyword);
-            } else if (r.matchConsumeIgnoreCase("SYSTEM")) {
+            } else if (r.matchConsumeIgnoreCase(DocumentType.SYSTEM_KEY)) {
+                t.doctypePending.pubSysKey = DocumentType.SYSTEM_KEY;
                 t.transition(AfterDoctypeSystemKeyword);
             } else {
                 t.error(this);
diff --git a/src/main/java/org/jsoup/parser/XmlTreeBuilder.java b/src/main/java/org/jsoup/parser/XmlTreeBuilder.java
index 2ac525fc59..cfcb1a34c6 100644
--- a/src/main/java/org/jsoup/parser/XmlTreeBuilder.java
+++ b/src/main/java/org/jsoup/parser/XmlTreeBuilder.java
@@ -97,7 +97,7 @@ void insert(Token.Character characterToken) {
     }
 
     void insert(Token.Doctype d) {
-        DocumentType doctypeNode = new DocumentType(settings.normalizeTag(d.getName()), d.getPublicIdentifier(), d.getSystemIdentifier(), baseUri);
+        DocumentType doctypeNode = new DocumentType(settings.normalizeTag(d.getName()), d.getPubSysKey(), d.getPublicIdentifier(), d.getSystemIdentifier(), baseUri);
         insertNode(doctypeNode);
     }
 
diff --git a/src/test/java/org/jsoup/nodes/DocumentTypeTest.java b/src/test/java/org/jsoup/nodes/DocumentTypeTest.java
index 12e6268ece..38110ff787 100644
--- a/src/test/java/org/jsoup/nodes/DocumentTypeTest.java
+++ b/src/test/java/org/jsoup/nodes/DocumentTypeTest.java
@@ -1,5 +1,7 @@
 package org.jsoup.nodes;
 
+import org.jsoup.Jsoup;
+import org.jsoup.parser.Parser;
 import org.junit.Test;
 
 import static org.junit.Assert.*;
@@ -38,4 +40,31 @@ public void constructorValidationOkWithBlankPublicAndSystemIds() {
         DocumentType combo = new DocumentType("notHtml", "--public", "--system", "");
         assertEquals("<!DOCTYPE notHtml PUBLIC \"--public\" \"--system\">", combo.outerHtml());
     }
+
+    @Test public void testRoundTrip() {
+        String base = "<!DOCTYPE html>";
+        assertEquals("<!doctype html>", htmlOutput(base));
+        assertEquals(base, xmlOutput(base));
+
+        String publicDoc = "<!DOCTYPE html PUBLIC \"-//W3C//DTD XHTML 1.0 Transitional//EN\" \"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd\">";
+        assertEquals(publicDoc, htmlOutput(publicDoc));
+        assertEquals(publicDoc, xmlOutput(publicDoc));
+
+        String systemDoc = "<!DOCTYPE html SYSTEM \"exampledtdfile.dtd\">";
+        assertEquals(systemDoc, htmlOutput(systemDoc));
+        assertEquals(systemDoc, xmlOutput(systemDoc));
+
+        String legacyDoc = "<!DOCTYPE html SYSTEM \"about:legacy-compat\">";
+        assertEquals(legacyDoc, htmlOutput(legacyDoc));
+        assertEquals(legacyDoc, xmlOutput(legacyDoc));
+    }
+
+    private String htmlOutput(String in) {
+        DocumentType type = (DocumentType) Jsoup.parse(in).childNode(0);
+        return type.outerHtml();
+    }
+
+    private String xmlOutput(String in) {
+        return Jsoup.parse(in, "", Parser.xmlParser()).childNode(0).outerHtml();
+    }
 }