diff --git a/release-notes/VERSION b/release-notes/VERSION
index 10bcd42d..27008b36 100644
--- a/release-notes/VERSION
+++ b/release-notes/VERSION
@@ -10,6 +10,9 @@ Project: woodstox
 
 5.3.1 (not yet released)
 
+#104: `NullPointerException` in `DTDValidator.validateElementEnd()`
+  for element undefined in DTD
+ (reported by ChrisTrenkamp@github)
 #105: W3CSchemaFactory constructor incorrectly references relaxng
 
 5.3.0 (15-Jul-2019)
diff --git a/src/main/java/com/ctc/wstx/dtd/DTDValidator.java b/src/main/java/com/ctc/wstx/dtd/DTDValidator.java
index d750320c..18862913 100644
--- a/src/main/java/com/ctc/wstx/dtd/DTDValidator.java
+++ b/src/main/java/com/ctc/wstx/dtd/DTDValidator.java
@@ -331,10 +331,10 @@ public int validateElementEnd(String localName, String uri, String prefix)
         throws XMLStreamException
     {
         // First, let's remove the top:
-        int ix = mElemCount-1;
-        /* [WSTX-200]: need to avoid problems when doing sub-tree
-         *   validation...
-         */
+        final int ix = mElemCount-1;
+
+        // [WSTX-200]: need to avoid problems when doing sub-tree
+        //   validation...
         if (ix < 0) {
             return XMLValidator.CONTENT_ALLOW_WS;
         }
@@ -359,7 +359,13 @@ public int validateElementEnd(String localName, String uri, String prefix)
             // doesn't really matter; epilog/prolog differently handled:
             return XMLValidator.CONTENT_ALLOW_WS;
         }
-        return mElems[ix-1].getAllowedContent();
+
+        final DTDElement element = mElems[ix-1];
+
+        // 22-Apr-2020, tatu: `null` validator added for unknown elements
+        return (element == null)
+                ? XMLValidator.CONTENT_ALLOW_ANY_TEXT
+                : element.getAllowedContent();
     }
 
     //public void validateText(String text, boolean lastTextSegment) ;
diff --git a/src/test/java/wstxtest/vstream/TestDTDErrorCollection104Test.java b/src/test/java/wstxtest/vstream/TestDTDErrorCollection104Test.java
new file mode 100644
index 00000000..739f42bf
--- /dev/null
+++ b/src/test/java/wstxtest/vstream/TestDTDErrorCollection104Test.java
@@ -0,0 +1,103 @@
+package wstxtest.vstream;
+
+import stax2.BaseStax2Test;
+
+import java.io.StringReader;
+import java.util.ArrayList;
+import java.util.List;
+
+import javax.xml.stream.*;
+
+import org.codehaus.stax2.XMLStreamReader2;
+import org.codehaus.stax2.validation.ValidationProblemHandler;
+import org.codehaus.stax2.validation.XMLValidationException;
+import org.codehaus.stax2.validation.XMLValidationProblem;
+import org.codehaus.stax2.validation.XMLValidationSchema;
+import org.codehaus.stax2.validation.XMLValidationSchemaFactory;
+
+public class TestDTDErrorCollection104Test
+    extends BaseStax2Test
+{
+    // [woodstox-core#103]
+    public void testValidationBeyondUnknownElement() throws Exception
+    {
+        final String DOC =
+                "<map>\n" + 
+                "  <val>\n" + 
+                "    <prop att=\"product\" val=\"win\" action=\"flag\" color=\"black\"/>\n" +
+                "  </val>\n" + 
+                "</map>\n";
+
+        final String INPUT_DTD =
+"<!ELEMENT map (notval+)>\n"
++"<!ELEMENT notval EMPTY>\n"
+;
+
+        XMLInputFactory f = getInputFactory();
+        setCoalescing(f, true);
+
+        XMLValidationSchemaFactory schemaFactory =
+                XMLValidationSchemaFactory.newInstance(XMLValidationSchema.SCHEMA_ID_DTD);
+        XMLValidationSchema schema = schemaFactory.createSchema(new StringReader(INPUT_DTD));
+        XMLStreamReader2 sr = (XMLStreamReader2)f.createXMLStreamReader(
+                new StringReader(DOC));
+
+        final List<XMLValidationProblem> probs = new ArrayList<XMLValidationProblem>();
+        
+        sr.validateAgainst(schema);
+        sr.setValidationProblemHandler(new ValidationProblemHandler() {
+            @Override
+            public void reportProblem(XMLValidationProblem problem)
+                    throws XMLValidationException {
+                probs.add(problem);
+            }
+        });
+
+        assertTokenType(START_ELEMENT, sr.next());
+        assertEquals("map", sr.getLocalName());
+
+        sr.next(); // SPACE or CHARACTERS
+        assertTokenType(START_ELEMENT, sr.next());
+        assertEquals("val", sr.getLocalName());
+        assertEquals(1, probs.size());
+        assertEquals("Undefined element <val> encountered", 
+                probs.get(0).getMessage());
+
+        sr.next(); // SPACE or CHARACTERS
+        assertEquals(1, probs.size());
+
+        // From this point on, however, behavior bit unclear except
+        // that for DTD I guess we can at least check for undefined
+        // cases....
+        
+        assertTokenType(START_ELEMENT, sr.next());
+        assertEquals("prop", sr.getLocalName());
+        // <prop> not defined either so:
+        assertEquals(2, probs.size());
+        assertEquals("Undefined element <prop> encountered", 
+                probs.get(1).getMessage());
+
+        assertTokenType(END_ELEMENT, sr.next());
+        assertEquals("prop", sr.getLocalName());
+        assertEquals(2, probs.size());
+
+        sr.next(); // SPACE or CHARACTERS
+        assertEquals(2, probs.size());
+        assertTokenType(END_ELEMENT, sr.next());
+        assertEquals("val", sr.getLocalName());
+        assertEquals(2, probs.size());
+        
+        sr.next(); // SPACE or CHARACTERS
+        assertTokenType(END_ELEMENT, sr.next());
+        assertEquals("map", sr.getLocalName());
+        assertEquals(3, probs.size());
+        assertEquals("Validation error, element </map>: Expected at least one element <notval>", 
+                probs.get(2).getMessage());
+
+        // Plus content model now missing <notval>(s)
+        assertTokenType(END_DOCUMENT, sr.next());
+        assertEquals(3, probs.size());
+
+        sr.close();
+    }
+}