diff --git a/src/main/java/org/apache/xmlbeans/impl/util/XsTypeConverter.java b/src/main/java/org/apache/xmlbeans/impl/util/XsTypeConverter.java
index 907fc199f..52cbf303a 100644
--- a/src/main/java/org/apache/xmlbeans/impl/util/XsTypeConverter.java
+++ b/src/main/java/org/apache/xmlbeans/impl/util/XsTypeConverter.java
@@ -17,6 +17,7 @@
 
 import org.apache.xmlbeans.*;
 import org.apache.xmlbeans.impl.common.InvalidLexicalValueException;
+import org.apache.xmlbeans.impl.common.XMLChar;
 
 import javax.xml.namespace.NamespaceContext;
 import javax.xml.namespace.QName;
@@ -482,6 +483,13 @@ public static QName lexQName(CharSequence charSeq, NamespaceContext nscontext) {
             localname = charSeq.toString();
         }
 
+        if (!prefix.isEmpty() && !XMLChar.isValidNCName(prefix)) {
+            throw new InvalidLexicalValueException("invalid xsd:QName '" + charSeq + "'");
+        }
+        if (!XMLChar.isValidNCName(localname)) {
+            throw new InvalidLexicalValueException("invalid xsd:QName '" + charSeq + "'");
+        }
+
         String uri = nscontext.getNamespaceURI(prefix);
 
         if (uri == null) {
diff --git a/src/test/java/misc/checkin/RichParserTests.java b/src/test/java/misc/checkin/RichParserTests.java
index f0c1049e5..1c74de7b1 100755
--- a/src/test/java/misc/checkin/RichParserTests.java
+++ b/src/test/java/misc/checkin/RichParserTests.java
@@ -83,6 +83,30 @@ void testInvalidBase64ThrowsInvalidLexicalValue() throws Exception {
         assertThrows(InvalidLexicalValueException.class, () -> attByName.getAttributeBase64Value("", "b"));
     }
 
+    @Test
+    void testInvalidQNameThrowsInvalidLexicalValue() throws Exception {
+        // The localname of an xsd:QName must be an NCName, so a value whose
+        // local part still contains a ':' (or any other non-NCName char) is
+        // outside the lexical space. lexQName resolved the prefix but never
+        // checked the parts, so "p:b:c" came back as QName{uri}b:c instead of
+        // being rejected like the holder validate path does.
+        XMLStreamReaderExt colonInLocal = atFirstStartElement("<a xmlns:p='urn:x'>p:b:c</a>");
+        assertThrows(InvalidLexicalValueException.class, colonInLocal::getQNameValue);
+
+        XMLStreamReaderExt spaceInLocal = atFirstStartElement("<a>b c</a>");
+        assertThrows(InvalidLexicalValueException.class, spaceInLocal::getQNameValue);
+
+        XMLStreamReaderExt emptyLocal = atFirstStartElement("<a xmlns:p='urn:x'>p:</a>");
+        assertThrows(InvalidLexicalValueException.class, emptyLocal::getQNameValue);
+
+        XMLStreamReaderExt attColon = atFirstStartElement("<a xmlns:p='urn:x' b='p:b:c'/>");
+        assertThrows(InvalidLexicalValueException.class, () -> attColon.getAttributeQNameValue(0));
+
+        // a well-formed prefixed QName still resolves
+        XMLStreamReaderExt good = atFirstStartElement("<a xmlns:p='urn:x'>p:good</a>");
+        assertEquals(new QName("urn:x", "good"), good.getQNameValue());
+    }
+
     private static XMLStreamReaderExt atFirstStartElement(String xml) throws Exception {
         XMLStreamReader xsr = XmlObject.Factory.parse(xml).newXMLStreamReader();
         XMLStreamReaderExt ext = new XMLStreamReaderExtImpl(xsr);