diff --git a/sources/OpenMcdf/CompoundFile.cs b/sources/OpenMcdf/CompoundFile.cs
index aadcc417..f706e118 100644
--- a/sources/OpenMcdf/CompoundFile.cs
+++ b/sources/OpenMcdf/CompoundFile.cs
@@ -1367,12 +1367,15 @@ int nextSecID
 
         private void EnsureUniqueSectorIndex(int nextSecID, HashSet<int> processedSectors)
         {
-            if (processedSectors.Contains(nextSecID) && this.validationExceptionEnabled)
+            if (!this.validationExceptionEnabled)
             {
-                throw new CFCorruptedFileException("The file is corrupted.");
+                return;
             }
 
-            processedSectors.Add(nextSecID);
+            if (!processedSectors.Add(nextSecID))
+            {
+                throw new CFCorruptedFileException("The file is corrupted.");
+            }
         }
 
         /// <summary>