Index: Ringtoets/Common/src/Ringtoets.Common.IO/Readers/ConfigurationReader.cs
===================================================================
diff -u -r8a00046f9112833f25944b0f2631c7003f7a1692 -r94587578a17566618ad7b26fc914d8b4d30fb99b
--- Ringtoets/Common/src/Ringtoets.Common.IO/Readers/ConfigurationReader.cs	(.../ConfigurationReader.cs)	(revision 8a00046f9112833f25944b0f2631c7003f7a1692)
+++ Ringtoets/Common/src/Ringtoets.Common.IO/Readers/ConfigurationReader.cs	(.../ConfigurationReader.cs)	(revision 94587578a17566618ad7b26fc914d8b4d30fb99b)
@@ -148,9 +148,10 @@
         /// <exception cref="CriticalFileReadException">Thrown when the provided XML document does not match the provided XML Schema Definition (XSD).</exception>
         private static void ValidateToSchema(XDocument document, string schemaString, string xmlFilePath)
         {
+            var xmlResourcesResolver = new XmlResourcesResolver();
             var xmlSchemaSet = new XmlSchemaSet
             {
-                XmlResolver = new XmlResourcesResolver()
+                XmlResolver = xmlResourcesResolver
             };
 
             try
@@ -163,6 +164,11 @@
                 throw new ArgumentException($"Invalid 'schemaString': {exception.Message}", exception);
             }
 
+            if (!xmlResourcesResolver.BaseSchemeReferenced)
+            {
+                throw new ArgumentException("Invalid 'schemaString': the base XML Schema Definition file 'ConfiguratieSchema.xsd' is not referenced.");
+            }
+
             try
             {
                 document.Validate(xmlSchemaSet, null);
@@ -229,11 +235,14 @@
                 }
             }
 
+            public bool BaseSchemeReferenced { get; private set; }
+
             public override object GetEntity(Uri absoluteUri, string role, Type ofObjectToReturn)
             {
                 switch (Path.GetFileName(absoluteUri.ToString()))
                 {
                     case "ConfiguratieSchema.xsd":
+                        BaseSchemeReferenced = true;
                         return new MemoryStream(Encoding.UTF8.GetBytes(Resources.ConfiguratieSchema));
                     case "StochastSchema.xsd":
                         return new MemoryStream(Encoding.UTF8.GetBytes(Resources.StochastSchema));