diff --git a/src/Umbraco.Web/PropertyEditors/FileUploadPropertyValueEditor.cs b/src/Umbraco.Web/PropertyEditors/FileUploadPropertyValueEditor.cs
index 81239caec0..942f53b561 100644
--- a/src/Umbraco.Web/PropertyEditors/FileUploadPropertyValueEditor.cs
+++ b/src/Umbraco.Web/PropertyEditors/FileUploadPropertyValueEditor.cs
@@ -99,7 +99,7 @@ namespace Umbraco.Web.PropertyEditors
         {
             // process the file
             // no file, invalid file, reject change
-            if (UploadFileTypeValidator.ValidateFileExtension(file.FileName) == false)
+            if (UploadFileTypeValidator.IsValidFileExtension(file.FileName) == false)
                 return null;
 
             // get the filepath
diff --git a/src/Umbraco.Web/PropertyEditors/ImageCropperPropertyValueEditor.cs b/src/Umbraco.Web/PropertyEditors/ImageCropperPropertyValueEditor.cs
index 7bea542521..a828f3a58f 100644
--- a/src/Umbraco.Web/PropertyEditors/ImageCropperPropertyValueEditor.cs
+++ b/src/Umbraco.Web/PropertyEditors/ImageCropperPropertyValueEditor.cs
@@ -142,7 +142,7 @@ namespace Umbraco.Web.PropertyEditors
         {
             // process the file
             // no file, invalid file, reject change
-            if (UploadFileTypeValidator.ValidateFileExtension(file.FileName) == false)
+            if (UploadFileTypeValidator.IsValidFileExtension(file.FileName) == false)
                 return null;
 
             // get the filepath
diff --git a/src/Umbraco.Web/PropertyEditors/UploadFileTypeValidator.cs b/src/Umbraco.Web/PropertyEditors/UploadFileTypeValidator.cs
index 5394aca5ba..6855ab3bb8 100644
--- a/src/Umbraco.Web/PropertyEditors/UploadFileTypeValidator.cs
+++ b/src/Umbraco.Web/PropertyEditors/UploadFileTypeValidator.cs
@@ -2,10 +2,10 @@
 using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
 using System.IO;
+using System.Linq;
 using Newtonsoft.Json.Linq;
 using Umbraco.Core;
 using Umbraco.Core.Services;
-using Umbraco.Core.Configuration;
 using Umbraco.Core.PropertyEditors;
 using Umbraco.Core.Configuration.UmbracoSettings;
 using Umbraco.Web.Composing;
@@ -16,13 +16,27 @@ namespace Umbraco.Web.PropertyEditors
     {
         public IEnumerable<ValidationResult> Validate(object value, string valueType, object dataTypeConfiguration)
         {
-            if (!(value is JObject jobject) || jobject["selectedFiles"] == null) yield break;
-
-            var fileNames = jobject["selectedFiles"].ToString().Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries);
-
-            foreach (var fileName in fileNames)
+            string selectedFiles = null;
+            if (value is JObject jobject && jobject["selectedFiles"] is JToken jToken)
             {
-                if (ValidateFileExtension(fileName) == false)
+                selectedFiles = jToken.ToString();
+            }
+            else if (valueType?.InvariantEquals(ValueTypes.String) == true)
+            {
+                selectedFiles = value as string;
+
+                if (string.IsNullOrWhiteSpace(selectedFiles))
+                    yield break;
+            }
+
+            var fileNames = selectedFiles?.Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries);
+
+            if (fileNames == null || !fileNames.Any())
+                yield break;
+
+            foreach (string filename in fileNames)
+            {
+                if (IsValidFileExtension(filename) == false)
                 {
                     //we only store a single value for this editor so the 'member' or 'field'
                     // we'll associate this error with will simply be called 'value'
@@ -30,11 +44,11 @@ namespace Umbraco.Web.PropertyEditors
                 }
             }
         }
-
-        internal static bool ValidateFileExtension(string fileName)
+        
+        internal static bool IsValidFileExtension(string fileName)
         {
             if (fileName.IndexOf('.') <= 0) return false;
-            var extension = Path.GetExtension(fileName).TrimStart(".");
+            var extension = new FileInfo(fileName).Extension.TrimStart(".");
             return Current.Configs.Settings().Content.IsFileAllowedForUpload(extension);
         }
     }