diff --git a/products/ASC.Files/Core/Core/Dao/TeamlabDao/FolderDao.cs b/products/ASC.Files/Core/Core/Dao/TeamlabDao/FolderDao.cs
index be035cdf81..dc9749f5c0 100644
--- a/products/ASC.Files/Core/Core/Dao/TeamlabDao/FolderDao.cs
+++ b/products/ASC.Files/Core/Core/Dao/TeamlabDao/FolderDao.cs
@@ -538,7 +538,7 @@ internal class FolderDao : AbstractDao, IFolderDao<int>
 
             var toDelete = await FilesDbContext.Tree
                 .AsQueryable()
-                .Where(r => subfolders.Keys.Contains(r.FolderId) && !subfolders.Keys.Contains(r.ParentId))
+                .Where(r => subfolders.ContainsKey(r.FolderId) && !subfolders.ContainsKey(r.ParentId))
                 .ToListAsync();
 
             FilesDbContext.Tree.RemoveRange(toDelete);
diff --git a/products/ASC.Files/Core/Core/FileStorageService.cs b/products/ASC.Files/Core/Core/FileStorageService.cs
index 532f6158ec..7744e93c9d 100644
--- a/products/ASC.Files/Core/Core/FileStorageService.cs
+++ b/products/ASC.Files/Core/Core/FileStorageService.cs
@@ -607,7 +607,7 @@ public class FileStorageService<T> //: IFileStorageService
         if (fileExt != _fileUtility.MasterFormExtension)
         {
             fileExt = _fileUtility.GetInternalExtension(title);
-            if (!_fileUtility.InternalExtension.Values.Contains(fileExt))
+            if (!_fileUtility.InternalExtension.ContainsValue(fileExt))
             {
                 fileExt = _fileUtility.InternalExtension[FileType.Document];
                 file.Title = title + fileExt;
diff --git a/products/ASC.Files/Core/HttpHandlers/FileHandler.ashx.cs b/products/ASC.Files/Core/HttpHandlers/FileHandler.ashx.cs
index 1df596d85d..d3eed85104 100644
--- a/products/ASC.Files/Core/HttpHandlers/FileHandler.ashx.cs
+++ b/products/ASC.Files/Core/HttpHandlers/FileHandler.ashx.cs
@@ -346,8 +346,7 @@ namespace ASC.Web.Files
 
                             var outType = (context.Request.Query[FilesLinkUtility.OutType].FirstOrDefault() ?? "").Trim();
                             if (!string.IsNullOrEmpty(outType)
-                                && FileUtility.ExtsConvertible.Keys.Contains(ext)
-                                && FileUtility.ExtsConvertible[ext].Contains(outType))
+                                && FileUtility.ExtsConvertible.ContainsKey(ext) && FileUtility.ExtsConvertible[ext].Contains(outType))
                             {
                                 ext = outType;
                             }
diff --git a/products/ASC.Files/Core/Utils/EntryManager.cs b/products/ASC.Files/Core/Utils/EntryManager.cs
index 91d7318e98..154943f0db 100644
--- a/products/ASC.Files/Core/Utils/EntryManager.cs
+++ b/products/ASC.Files/Core/Utils/EntryManager.cs
@@ -1162,8 +1162,7 @@ public class EntryManager
 
         if (file.ProviderEntry && !newExtension.Equals(currentExt))
         {
-            if (_fileUtility.ExtsConvertible.Keys.Contains(newExtension)
-                && _fileUtility.ExtsConvertible[newExtension].Contains(currentExt))
+            if (_fileUtility.ExtsConvertible.ContainsKey(newExtension) && _fileUtility.ExtsConvertible[newExtension].Contains(currentExt))
             {
                 if (stream != null)
                 {
diff --git a/products/ASC.Files/Core/Utils/FileConverter.cs b/products/ASC.Files/Core/Utils/FileConverter.cs
index 9bda33f382..2ab80a514c 100644
--- a/products/ASC.Files/Core/Utils/FileConverter.cs
+++ b/products/ASC.Files/Core/Utils/FileConverter.cs
@@ -177,7 +177,7 @@ internal class FileConverterQueue<T> : IDisposable
 
                         lock (_locker)
                         {
-                            if (!_conversionQueue.Keys.Contains(file))
+                            if (!_conversionQueue.ContainsKey(file))
                             {
                                 continue;
                             }
@@ -632,12 +632,12 @@ public class FileConverter
         }
 
         fileExtension = FileUtility.GetFileExtension(file.Title);
-        if (_fileUtility.InternalExtension.Values.Contains(toExtension))
+        if (_fileUtility.InternalExtension.ContainsValue(toExtension))
         {
             return true;
         }
 
-        return _fileUtility.ExtsConvertible.Keys.Contains(fileExtension) && _fileUtility.ExtsConvertible[fileExtension].Contains(toExtension);
+        return _fileUtility.ExtsConvertible.ContainsKey(fileExtension) && _fileUtility.ExtsConvertible[fileExtension].Contains(toExtension);
     }
 
     public Task<Stream> ExecAsync<T>(File<T> file)
@@ -748,7 +748,7 @@ public class FileConverter
         {
             throw new ArgumentException(FilesCommonResource.ErrorMassage_NotSupportedFormat);
         }
-        if (!string.IsNullOrEmpty(file.ConvertedType) || _fileUtility.InternalExtension.Values.Contains(FileUtility.GetFileExtension(file.Title)))
+        if (!string.IsNullOrEmpty(file.ConvertedType) || _fileUtility.InternalExtension.ContainsValue(FileUtility.GetFileExtension(file.Title)))
         {
             return;
         }