diff --git a/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.C b/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.C
index 95c5360b8f..5b3fbe67c7 100644
--- a/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.C
+++ b/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.C
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2017-2018 OpenFOAM Foundation
-    Copyright (C) 2019-2024 OpenCFD Ltd.
+    Copyright (C) 2019-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -867,7 +867,7 @@ off_t Foam::fileOperations::masterUncollatedFileOperation::fileSize
     const bool followLink
 ) const
 {
-    return masterOp<off_t>
+    return masterOp<fileSizeOp::value_type>
     (
         fName,
         fileSizeOp(followLink),
diff --git a/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.H b/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.H
index e3a8886394..58d85a8897 100644
--- a/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.H
+++ b/src/OpenFOAM/global/fileOperations/masterUncollatedFileOperation/masterUncollatedFileOperation.H
@@ -6,7 +6,7 @@
      \\/     M anipulation  |
 -------------------------------------------------------------------------------
     Copyright (C) 2017 OpenFOAM Foundation
-    Copyright (C) 2019-2024 OpenCFD Ltd.
+    Copyright (C) 2019-2025 OpenCFD Ltd.
 -------------------------------------------------------------------------------
 License
     This file is part of OpenFOAM.
@@ -222,14 +222,26 @@ protected:
         {
             const bool followLink_;
         public:
-            fileSizeOp(const bool followLink)
+
+            #ifdef _WIN32
+            // off_t is 'long int' for windows (missing pTraits)
+            typedef int64_t value_type;
+            #else
+            typedef off_t value_type;
+            #endif
+
+            fileSizeOp(bool followLink) noexcept
             :
                 followLink_(followLink)
             {}
 
-            off_t operator()(const fileName& f) const
+            auto operator()(const fileName& f) const
             {
+                #ifdef _WIN32
+                return value_type(Foam::fileSize(f, followLink_));
+                #else
                 return Foam::fileSize(f, followLink_);
+                #endif
             }
         };