diff --git a/bin/trace b/bin/trace
index d37c87a596b..4585adcf70f 100755
--- a/bin/trace
+++ b/bin/trace
@@ -121,6 +121,7 @@ $Source = "";
                "H5M_iterate_t"              => 'MI',
                "H5FD_mem_t"                 => "Mt",
                "off_t"                      => "o",
+               "HDoff_t"                    => "Ho",
                "H5O_iterate1_t"             => "Oi",
                "H5O_iterate2_t"             => "OI",
                "H5O_mcdt_search_cb_t"       => "Os",
diff --git a/release_docs/RELEASE.txt b/release_docs/RELEASE.txt
index 121b1adda45..0e5d3cdd7a6 100644
--- a/release_docs/RELEASE.txt
+++ b/release_docs/RELEASE.txt
@@ -425,6 +425,22 @@ New Features
 
     Library:
     --------
+    - H5Pset_external() now uses HDoff_t, which is always a 64-bit type
+
+      The H5Pset_external() call took an off_t parameter in HDF5 1.14.x and
+      earlier. On POSIX systems, off_t is specified as a 64-bit type via
+      POSIX large-file support (LFS). On Windows, however, off_t is defined
+      as a 32-bit type, even on 64-bit Windows.
+
+      HDoff_t has been added to H5public.h and is defined to be __int64 on
+      Windows and the library has been updated to use HDoff_t in place of
+      off_t throughout. The H5Pset_external() offset parameter has also been
+      updated to be HDoff_t.
+
+      There is no API compatibility wrapper for this change.
+
+      Fixes GitHub issue #3506
+
     - Relaxed behavior of H5Pset_page_buffer_size() when opening files
 
       This API call sets the size of a file's page buffer cache. This call
diff --git a/src/H5Pdcpl.c b/src/H5Pdcpl.c
index a5b7872549d..5cb85cb7478 100644
--- a/src/H5Pdcpl.c
+++ b/src/H5Pdcpl.c
@@ -2586,7 +2586,7 @@ H5Pget_chunk_opts(hid_t plist_id, unsigned *options /*out*/)
  *-------------------------------------------------------------------------
  */
 herr_t
-H5Pset_external(hid_t plist_id, const char *name, off_t offset, hsize_t size)
+H5Pset_external(hid_t plist_id, const char *name, HDoff_t offset, hsize_t size)
 {
     size_t          idx;
     hsize_t         total, tmp;
@@ -2616,8 +2616,8 @@ H5Pset_external(hid_t plist_id, const char *name, off_t offset, hsize_t size)
             tmp = total + efl.slot[idx].size;
             if (tmp <= total)
                 HGOTO_ERROR(H5E_EFL, H5E_OVERFLOW, FAIL, "total external data size overflowed");
-        } /* end for */
-    }     /* end if */
+        }
+    }
 
     /* Add to the list */
     if (efl.nused >= efl.nalloc) {
@@ -2628,7 +2628,8 @@ H5Pset_external(hid_t plist_id, const char *name, off_t offset, hsize_t size)
             HGOTO_ERROR(H5E_RESOURCE, H5E_CANTALLOC, FAIL, "memory allocation failed");
         efl.nalloc = na;
         efl.slot   = x;
-    } /* end if */
+    }
+
     idx                       = efl.nused;
     efl.slot[idx].name_offset = 0; /*not entered into heap yet*/
     efl.slot[idx].name        = H5MM_xstrdup(name);
diff --git a/src/H5Ppublic.h b/src/H5Ppublic.h
index e3d574fc9a4..48f6098af58 100644
--- a/src/H5Ppublic.h
+++ b/src/H5Ppublic.h
@@ -5678,6 +5678,7 @@ H5_DLL herr_t H5Pget_mpi_params(hid_t fapl_id, MPI_Comm *comm, MPI_Info *info);
  */
 H5_DLL herr_t H5Pset_mpi_params(hid_t fapl_id, MPI_Comm comm, MPI_Info info);
 #endif /* H5_HAVE_PARALLEL */
+
 /**
  * \ingroup FAPL
  *
@@ -6532,7 +6533,7 @@ H5_DLL herr_t H5Pset_dset_no_attrs_hint(hid_t dcpl_id, hbool_t minimize);
  * \since 1.0.0
  *
  */
-H5_DLL herr_t H5Pset_external(hid_t plist_id, const char *name, off_t offset, hsize_t size);
+H5_DLL herr_t H5Pset_external(hid_t plist_id, const char *name, HDoff_t offset, hsize_t size);
 /**
  * \ingroup DCPL
  *
diff --git a/src/H5private.h b/src/H5private.h
index 9521d5041a9..c7a622ebd22 100644
--- a/src/H5private.h
+++ b/src/H5private.h
@@ -657,16 +657,19 @@ typedef struct {
  */
 #include "H5win32defs.h"
 
-/* Platform-independent definitions for struct stat and off_t */
-#ifndef H5_HAVE_WIN32_API
-/* These definitions differ in Windows and are defined in
- * H5win32defs for that platform.
+/* Platform-independent definition for struct stat. For Win32, see
+ * H5win32defs.h.
  */
+#ifndef H5_HAVE_WIN32_API
 typedef struct stat h5_stat_t;
-typedef off_t       h5_stat_size_t;
-#define HDoff_t off_t
 #endif
 
+/* __int64 is the correct type for the st_size field of the _stati64
+ * struct on Windows (MSDN isn't very clear about this). POSIX systems use
+ * off_t. Both of these are typedef'd to HDoff_t in H5public.h.
+ */
+typedef HDoff_t h5_stat_size_t;
+
 /* Redefinions of some POSIX and C functions (mainly to deal with Windows) */
 
 #ifndef HDaccess
diff --git a/src/H5public.h b/src/H5public.h
index 8798e78dd72..7551e088ffe 100644
--- a/src/H5public.h
+++ b/src/H5public.h
@@ -300,6 +300,22 @@ typedef long long ssize_t;
  */
 typedef uint64_t hsize_t;
 
+/* off_t exists on Windows, but is always a 32-bit long, even on 64-bit Windows,
+ * so on Windows we define HDoff_t to be __int64, which is the type of the
+ * st_size field of the _stati64 struct.
+ */
+#ifdef H5_HAVE_WIN32_API
+/**
+ * Platform-independent offset
+ */
+typedef __int64 HDoff_t;
+#else
+/**
+ * Platform-independent offset
+ */
+typedef off_t HDoff_t;
+#endif
+
 #ifdef H5_HAVE_PARALLEL
 #define HSIZE_AS_MPI_TYPE MPI_UINT64_T
 #endif
diff --git a/src/H5win32defs.h b/src/H5win32defs.h
index a996f60ab01..72d0e556157 100644
--- a/src/H5win32defs.h
+++ b/src/H5win32defs.h
@@ -20,17 +20,10 @@
 
 #ifdef H5_HAVE_WIN32_API
 
-/* off_t exists on Windows, but is always a 32-bit long, even on 64-bit Windows,
- * so we define HDoff_t to be __int64, which is the type of the st_size field
- * of the _stati64 struct and what is returned by _ftelli64().
- */
-#define HDoff_t __int64
-
-/* __int64 is the correct type for the st_size field of the _stati64 struct.
- * MSDN isn't very clear about this.
+/* Win32 platform-independent definition for struct stat. For POSIX, see
+ * H5private.h.
  */
 typedef struct _stati64 h5_stat_t;
-typedef __int64         h5_stat_size_t;
 
 #ifdef H5_HAVE_VISUAL_STUDIO
 struct timezone {