Index: Ringtoets/Common/src/Ringtoets.Common.IO/Readers/ConfigurationReader.cs
===================================================================
diff -u -r4136a0156ea9e20e7e1aca569c5e89cbc713fed2 -r9adb7863b832fbef7249803d20750688061c846e
--- Ringtoets/Common/src/Ringtoets.Common.IO/Readers/ConfigurationReader.cs	(.../ConfigurationReader.cs)	(revision 4136a0156ea9e20e7e1aca569c5e89cbc713fed2)
+++ Ringtoets/Common/src/Ringtoets.Common.IO/Readers/ConfigurationReader.cs	(.../ConfigurationReader.cs)	(revision 9adb7863b832fbef7249803d20750688061c846e)
@@ -50,7 +50,13 @@
         /// </summary>
         /// <param name="xmlFilePath">The file path to the XML file.</param>
         /// <param name="schemaString">A string representing an XML Schema Definition (XSD).</param>
-        /// <exception cref="ArgumentException">Thrown when <paramref name="xmlFilePath"/> is invalid.</exception>
+        /// <exception cref="ArgumentException">Thrown when:
+        /// <list type="bullet">
+        /// <item><paramref name="xmlFilePath"/> is invalid.</item>
+        /// <item><paramref name="schemaString"/> is <c>null</c> or empty.</item>
+        /// <item><paramref name="schemaString"/> contains an invalid schema definition.</item>
+        /// </list>
+        /// </exception>
         /// <exception cref="CriticalFileReadException">Thrown when:
         /// <list type="bullet">
         /// <item><paramref name="xmlFilePath"/> points to a file that does not exist.</item>
@@ -62,6 +68,11 @@
         {
             IOUtils.ValidateFilePath(xmlFilePath);
 
+            if (string.IsNullOrWhiteSpace(schemaString))
+            {
+                throw new ArgumentException(nameof(schemaString));
+            }
+
             ValidateFileExists(xmlFilePath);
 
             xmlDocument = LoadDocument(xmlFilePath);
@@ -136,10 +147,19 @@
         private static void ValidateToSchema(XDocument document, string schemaString, string xmlFilePath)
         {
             var xmlSchemaSet = new XmlSchemaSet();
-            xmlSchemaSet.Add(XmlSchema.Read(new StringReader(schemaString), null));
 
             try
             {
+                xmlSchemaSet.Add(XmlSchema.Read(new StringReader(schemaString), null));
+            }
+            catch (Exception exception) when (exception is XmlException
+                                              || exception is XmlSchemaException)
+            {
+                throw new ArgumentException($"Invalid 'schemaString': {exception.Message}", exception);
+            }
+
+            try
+            {
                 document.Validate(xmlSchemaSet, null);
             }
             catch (XmlSchemaValidationException exception)