diff --git a/programs/fileio.c b/programs/fileio.c
index 6fbe0c8ed..dc5d95b39 100644
--- a/programs/fileio.c
+++ b/programs/fileio.c
@@ -687,16 +687,17 @@ static void FIO_getDictFileStat(const char* fileName, stat_t* dictFileStat) {
     }
 }
 
-/*  FIO_createDictBuffer() :
- *  creates a buffer, pointed by `*bufferPtr`,
+/*  FIO_setDictBufferMalloc() :
+ *  allocates a buffer, pointed by `dict->dictBuffer`,
  *  loads `filename` content into it, up to DICTSIZE_MAX bytes.
  * @return : loaded size
  *  if fileName==NULL, returns 0 and a NULL pointer
  */
-static size_t FIO_createDictBuffer(void** bufferPtr, const char* fileName, FIO_prefs_t* const prefs, stat_t* dictFileStat)
+static size_t FIO_setDictBufferMalloc(FIO_Dict_t* dict, const char* fileName, FIO_prefs_t* const prefs, stat_t* dictFileStat)
 {
     FILE* fileHandle;
     U64 fileSize;
+    void** bufferPtr = &dict->dictBuffer;
 
     assert(bufferPtr != NULL);
     assert(dictFileStat != NULL);
@@ -733,20 +734,17 @@ static size_t FIO_createDictBuffer(void** bufferPtr, const char* fileName, FIO_p
 
 #if (PLATFORM_POSIX_VERSION > 0)
 #include <sys/mman.h>
-static void* FIO_mmap(size_t fileSize, int fileHandle)
+static void FIO_munmap(FIO_Dict_t* dict)
 {
-    return mmap
-    (NULL, (size_t)fileSize, PROT_READ, MAP_PRIVATE, fileHandle, 0);
+    munmap(dict->dictBuffer, dict->dictBufferSize);
+    dict->dictBuffer = NULL;
+    dict->dictBufferSize = 0;
 }
-static int FIO_munmap(void* buffer, size_t bufferSize)
-{
-    return munmap(buffer, bufferSize);
-}
-/* We might want to also do mapping for windows */
-static size_t FIO_createDictBufferMMap(void** bufferPtr, const char* fileName, FIO_prefs_t* const prefs, stat_t* dictFileStat)
+static size_t FIO_setDictBufferMMap(FIO_Dict_t* dict, const char* fileName, FIO_prefs_t* const prefs, stat_t* dictFileStat)
 {
     int fileHandle;
     U64 fileSize;
+    void** bufferPtr = &dict->dictBuffer;
 
     assert(bufferPtr != NULL);
     assert(dictFileStat != NULL);
@@ -770,27 +768,90 @@ static size_t FIO_createDictBufferMMap(void** bufferPtr, const char* fileName, F
         }
     }
 
-    *bufferPtr = FIO_mmap((size_t)fileSize, fileHandle);
+    *bufferPtr = mmap(NULL, (size_t)fileSize, PROT_READ, MAP_PRIVATE, fileHandle, 0);
+    if (*bufferPtr==NULL) EXM_THROW(34, "%s", strerror(errno));
 
     close(fileHandle);
     return (size_t)fileSize;
 }
-#else
-static size_t FIO_createDictBufferMMap(void** bufferPtr, const char* fileName, FIO_prefs_t* const prefs, stat_t* dictFileStat)
+#elif defined(_MSC_VER) || defined(_WIN32)
+#include <windows.h>
+static void FIO_munmap(FIO_Dict_t* dict)
 {
-   return FIO_createDictBuffer(bufferPtr, fileName, prefs, dictFileStat);
+    UnmapViewOfFile(dict->dictBuffer);
+    CloseHandle(dict->dictHandle);
+    dict->dictBuffer = NULL;
+    dict->dictBufferSize = 0;
 }
-static void FIO_munmap(void* buffer, size_t bufferSize) {
-   (void)bufferSize;
-   free(buffer);
+static size_t FIO_setDictBufferMMap(FIO_Dict_t* dict, const char* fileName, FIO_prefs_t* const prefs, stat_t* dictFileStat)
+{
+    HANDLE fileHandle, mapping;
+    U64 fileSize;
+    void** bufferPtr = &dict->dictBuffer;
+
+    assert(bufferPtr != NULL);
+    assert(dictFileStat != NULL);
+    *bufferPtr = NULL;
+    if (fileName == NULL) return 0;
+
+    DISPLAYLEVEL(4,"Loading %s as dictionary \n", fileName);
+
+    fileHandle = CreateFileA(fileName, GENERIC_READ, FILE_SHARE_READ, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_READONLY, NULL);
+
+    if (fileHandle == INVALID_HANDLE_VALUE) {
+        EXM_THROW(33, "Couldn't open dictionary %s: %s", fileName, strerror(errno));
+    }
+
+    fileSize = UTIL_getFileSizeStat(dictFileStat);
+    {
+        size_t const dictSizeMax = prefs->patchFromMode ? prefs->memLimit : DICTSIZE_MAX;
+        if (fileSize >  dictSizeMax) {
+            EXM_THROW(34, "Dictionary file %s is too large (> %u bytes)",
+                            fileName,  (unsigned)dictSizeMax);   /* avoid extreme cases */
+        }
+    }
+
+    mapping = CreateFileMapping(fileHandle, NULL, PAGE_READONLY, 0, 0, NULL);
+	if (mapping == NULL) {
+        EXM_THROW(35, "Couldn't map dictionary %s: %s", fileName, strerror(errno));
+    }
+
+	*bufferPtr = MapViewOfFile(mapping, FILE_MAP_READ, 0, 0, (DWORD)fileSize); /* we can only cast to DWORD here because dictSize <= 2GB */
+	if (*bufferPtr==NULL) EXM_THROW(36, "%s", strerror(errno));
+
+    dict->dictHandle = fileHandle;
+    return (size_t)fileSize;
+}
+#else
+static size_t FIO_setDictBufferMMap(FIO_Dict_t* dict, const char* fileName, FIO_prefs_t* const prefs, stat_t* dictFileStat)
+{
+   return FIO_setDictBufferMalloc(dict, fileName, prefs, dictFileStat);
+}
+static void FIO_munmap(FIO_Dict_t* dict) {
+   free(dict->dictBuffer);
+   dict->dictBuffer = NULL;
+   dict->dictBufferSize = 0;
 }
 #endif
 
-static void FIO_freeDict(const FIO_Dict_t* dict) {
+static void FIO_freeDict(FIO_Dict_t* dict) {
     if (dict->dictBufferType == FIO_mallocDict) {
         free(dict->dictBuffer);
+        dict->dictBuffer = NULL;
+        dict->dictBufferSize = 0;
     } else if (dict->dictBufferType == FIO_mmapDict)  {
-        FIO_munmap(dict->dictBuffer, dict->dictBufferSize);
+        FIO_munmap(dict);
+    } else {
+        assert(0); /* Should not reach this case */
+    }
+}
+
+static void FIO_initDict(FIO_Dict_t* dict, const char* fileName, FIO_prefs_t* const prefs, stat_t* dictFileStat, FIO_dictBufferType_t dictBufferType) {
+    dict->dictBufferType = dictBufferType;
+    if (dict->dictBufferType == FIO_mallocDict) {
+        dict->dictBufferSize = FIO_setDictBufferMalloc(dict, fileName, prefs, dictFileStat);
+    } else if (dict->dictBufferType == FIO_mmapDict)  {
+        dict->dictBufferSize = FIO_setDictBufferMMap(dict, fileName, prefs, dictFileStat);
     } else {
         assert(0); /* Should not reach this case */
     }
@@ -1045,6 +1106,7 @@ static cRess_t FIO_createCResources(FIO_prefs_t* const prefs,
                                     int cLevel, ZSTD_compressionParameters comprParams) {
     int useMMap = prefs->mmapDict == ZSTD_ps_enable;
     int forceNoUseMMap = prefs->mmapDict == ZSTD_ps_disable;
+    FIO_dictBufferType_t dictBufferType;
     cRess_t ress;
     memset(&ress, 0, sizeof(ress));
 
@@ -1065,13 +1127,8 @@ static cRess_t FIO_createCResources(FIO_prefs_t* const prefs,
         FIO_adjustParamsForPatchFromMode(prefs, &comprParams, dictSize, ssSize > 0 ? ssSize : maxSrcFileSize, cLevel);
     }
 
-    ress.dict.dictBufferType = (useMMap && !forceNoUseMMap) ? FIO_mmapDict : FIO_mallocDict;
-
-    if (ress.dict.dictBufferType == FIO_mallocDict) {
-        ress.dict.dictBufferSize = FIO_createDictBuffer(&ress.dict.dictBuffer, dictFileName, prefs, &ress.dictFileStat);   /* works with dictFileName==NULL */
-    } else {
-        ress.dict.dictBufferSize = FIO_createDictBufferMMap(&ress.dict.dictBuffer, dictFileName, prefs, &ress.dictFileStat);
-    }
+    dictBufferType = (useMMap && !forceNoUseMMap) ? FIO_mmapDict : FIO_mallocDict;
+    FIO_initDict(&ress.dict, dictFileName, prefs, &ress.dictFileStat, dictBufferType);   /* works with dictFileName==NULL */
 
     ress.writeCtx = AIO_WritePool_create(prefs, ZSTD_CStreamOutSize());
     ress.readCtx = AIO_ReadPool_create(prefs, ZSTD_CStreamInSize());
@@ -1135,7 +1192,7 @@ static cRess_t FIO_createCResources(FIO_prefs_t* const prefs,
     return ress;
 }
 
-static void FIO_freeCResources(const cRess_t* const ress)
+static void FIO_freeCResources(cRess_t* const ress)
 {
     FIO_freeDict(&(ress->dict));
     AIO_WritePool_free(ress->writeCtx);
@@ -1976,7 +2033,7 @@ int FIO_compressFilename(FIO_ctx_t* const fCtx, FIO_prefs_t* const prefs, const
                          const char* srcFileName, const char* dictFileName,
                          int compressionLevel, ZSTD_compressionParameters comprParams)
 {
-    cRess_t const ress = FIO_createCResources(prefs, dictFileName, UTIL_getFileSize(srcFileName), compressionLevel, comprParams);
+    cRess_t ress = FIO_createCResources(prefs, dictFileName, UTIL_getFileSize(srcFileName), compressionLevel, comprParams);
     int const result = FIO_compressFilename_srcFile(fCtx, prefs, ress, dstFileName, srcFileName, compressionLevel);
 
 #define DISPLAY_LEVEL_DEFAULT 2
@@ -2169,7 +2226,6 @@ static dRess_t FIO_createDResources(FIO_prefs_t* const prefs, const char* dictFi
     }
 
     /* Allocation */
-    ress.dict.dictBufferType = (useMMap && !forceNoUseMMap) ? FIO_mmapDict : FIO_mallocDict;
     ress.dctx = ZSTD_createDStream();
     if (ress.dctx==NULL)
         EXM_THROW(60, "Error: %s : can't create ZSTD_DStream", strerror(errno));
@@ -2177,11 +2233,9 @@ static dRess_t FIO_createDResources(FIO_prefs_t* const prefs, const char* dictFi
     CHECK( ZSTD_DCtx_setParameter(ress.dctx, ZSTD_d_forceIgnoreChecksum, !prefs->checksumFlag));
 
     /* dictionary */
-    {   if (ress.dict.dictBufferType == FIO_mallocDict) {
-            ress.dict.dictBufferSize = FIO_createDictBuffer(&ress.dict.dictBuffer, dictFileName, prefs, &statbuf);
-        } else {
-            ress.dict.dictBufferSize = FIO_createDictBufferMMap(&ress.dict.dictBuffer, dictFileName, prefs, &statbuf);
-        }
+    {
+        FIO_dictBufferType_t dictBufferType = (useMMap && !forceNoUseMMap) ? FIO_mmapDict : FIO_mallocDict;
+        FIO_initDict(&ress.dict, dictFileName, prefs, &statbuf, dictBufferType);
 
         CHECK(ZSTD_DCtx_reset(ress.dctx, ZSTD_reset_session_only) );
 
diff --git a/programs/fileio_types.h b/programs/fileio_types.h
index e85abd477..2994a6092 100644
--- a/programs/fileio_types.h
+++ b/programs/fileio_types.h
@@ -78,6 +78,9 @@ typedef struct {
     void* dictBuffer;
     size_t dictBufferSize;
     FIO_dictBufferType_t dictBufferType;
+#if defined(_MSC_VER) || defined(_WIN32)
+    HANDLE dictHandle;
+#endif
 } FIO_Dict_t;
 
 #endif /* FILEIO_TYPES_HEADER */