diff --git a/src/DocumentFormat.OpenXml.Framework/MCContext.cs b/src/DocumentFormat.OpenXml.Framework/MCContext.cs
index db28a2e1b..e3e91c654 100644
--- a/src/DocumentFormat.OpenXml.Framework/MCContext.cs
+++ b/src/DocumentFormat.OpenXml.Framework/MCContext.cs
@@ -138,8 +138,8 @@ internal IEnumerable<XmlQualifiedName> ParseQNameList(string qnameList, OnInvali
 
             foreach (var qname in qnames)
             {
-                var items = qname.Split(':');
-                if (items.Length != 2)
+                var colonIndex = qname.IndexOf(":", StringComparison.Ordinal);
+                if (colonIndex <= 0 || colonIndex == qname.Length - 1 || qname.IndexOf(":", colonIndex + 1, StringComparison.Ordinal) >= 0)
                 {
                     if (onInvalidQName(qnameList))
                     {
@@ -151,7 +151,7 @@ internal IEnumerable<XmlQualifiedName> ParseQNameList(string qnameList, OnInvali
                     }
                 }
 
-                var ns = LookupNamespaceDelegate?.Invoke(items[0]);
+                var ns = LookupNamespaceDelegate?.Invoke(qname.Substring(0, colonIndex));
                 if (ns.IsNullOrEmpty())
                 {
                     if (onInvalidQName(qnameList))
@@ -164,7 +164,7 @@ internal IEnumerable<XmlQualifiedName> ParseQNameList(string qnameList, OnInvali
                     }
                 }
 
-                yield return new XmlQualifiedName(items[1], ns);
+                yield return new XmlQualifiedName(qname.Substring(colonIndex + 1), ns);
             }
         }
 
diff --git a/src/DocumentFormat.OpenXml.Framework/Validation/Schema/CompatibilityRuleAttributesValidator.cs b/src/DocumentFormat.OpenXml.Framework/Validation/Schema/CompatibilityRuleAttributesValidator.cs
index 745c4f102..2b9288db7 100644
--- a/src/DocumentFormat.OpenXml.Framework/Validation/Schema/CompatibilityRuleAttributesValidator.cs
+++ b/src/DocumentFormat.OpenXml.Framework/Validation/Schema/CompatibilityRuleAttributesValidator.cs
@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
+using System;
 using System.Collections.Generic;
 
 namespace DocumentFormat.OpenXml.Validation.Schema
@@ -189,14 +190,14 @@ internal static void ValidateMcAttributes(ValidationContext validationContext)
                 }
 
                 // must be QName
-                var items = qname.Value.Split(':');
-                if (items.Length != 2)
+                var colonIndex = qname.Value.IndexOf(":", StringComparison.Ordinal);
+                if (colonIndex <= 0 || colonIndex == qname.Value.Length - 1 || qname.Value.IndexOf(":", colonIndex + 1, StringComparison.Ordinal) >= 0)
                 {
                     return qname;
                 }
 
                 // Prefix must be already defined.
-                var attributeNamesapce = element.LookupNamespace(items[0]);
+                var attributeNamesapce = element.LookupNamespace(qname.Value.Substring(0, colonIndex));
                 if (attributeNamesapce.IsNullOrEmpty())
                 {
                     return qname;