diff --git a/CMakeLists.txt b/CMakeLists.txt
index fb9196b87..118c15f90 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -151,7 +151,6 @@ endif()
 ecbuild_add_option( FEATURE MEMFS
     DESCRIPTION "Memory based access to definitions/samples"
     DEFAULT OFF
-    CONDITION ECCODES_HAVE_FMEMOPEN OR ECCODES_HAVE_FUNOPEN OR (EC_OS_NAME MATCHES "windows")
     REQUIRED_PACKAGES PythonInterp )
 
 #if( HAVE_MEMFS AND "${CMAKE_C_COMPILER_ID}" STREQUAL "Cray")
diff --git a/memfs.py b/memfs.py
index 642849cb2..428063633 100755
--- a/memfs.py
+++ b/memfs.py
@@ -107,7 +107,7 @@ for directory in dirs:
                 # e.g. 23 -> 0x23
                 for n in range(0, len(contents_hex), 2):
                     twoChars = ascii(contents_hex[n : n + 2])
-                    
+
                     buffer.write(encode("0x%s," % (twoChars,)))
 
                     i += 1
@@ -130,195 +130,32 @@ opath = output_file_base + "_final.c"
 print("MEMFS: Generating output:", opath)
 g = open(opath, "w")
 
-print(
-    """
-#include "eccodes_config.h"
-#ifdef ECCODES_HAVE_FMEMOPEN
-#define _GNU_SOURCE
-#endif
+f = open(os.path.join(os.path.dirname(__file__), "src", "memfs.c"))
+for line in f.readlines():
+    line = line.rstrip()
+    if "<MARKER>" in line:
+        # Write extern variables with sizes
+        for k, v in SIZES.items():
+            print("extern const unsigned char %s[%d];" % (k, v), file=g)
 
-#include <stdio.h>
-#include <stdlib.h>
-#include <errno.h>
-#include <string.h>
-#include "eccodes_windef.h"
-""",
-    file=g,
-)
+        print(
+            "static struct entry entries[] = {",
+            file=g,
+        )
+        items = [(v, k) for k, v in FILES.items()]
+        for k, v in sorted(items):
+            print(
+                '{"/MEMFS%s", &%s[0], sizeof(%s) / sizeof(%s[0]) },' % (k, v, v, v),
+                file=g,
+            )
+        print(
+            "};",
+            file=g,
+        )
 
-# Write extern variables with sizes
-for k, v in SIZES.items():
-    print("extern const unsigned char %s[%d];" % (k, v), file=g)
+    else:
+        print(line, file=g)
 
-print(
-    """
-struct entry {
-    const char* path;
-    const unsigned char* content;
-    size_t length;
-} entries[] = { """,
-    file=g,
-)
-
-items = [(v, k) for k, v in FILES.items()]
-
-for k, v in sorted(items):
-    print('{"/MEMFS%s", &%s[0], sizeof(%s) / sizeof(%s[0]) },' % (k, v, v, v), file=g)
-
-
-print(
-    """};
-
-#if defined(ECCODES_HAVE_FUNOPEN) && !defined(ECCODES_HAVE_FMEMOPEN)
-
-typedef struct mem_file {
-    const char* buffer;
-    size_t size;
-    size_t pos;
-} mem_file;
-
-static int read_mem(void *data, char * buf, int len) {
-    mem_file* f = (mem_file*)data;
-    int n = len;
-
-    if(f->pos + n > f->size) {
-        n = f->size - f->pos;
-    }
-
-    memcpy(buf, f->buffer + f->pos, n);
-
-    f->pos += n;
-    return n;
-}
-
-static int write_mem(void* data, const char* buf, int len) {
-    mem_file* f = (mem_file*)data;
-    return -1;
-}
-
-static fpos_t seek_mem(void *data, fpos_t pos, int whence) {
-    mem_file* f = (mem_file*)data;
-    long newpos = 0;
-
-    switch (whence) {
-    case SEEK_SET:
-        newpos = (long)pos;
-        break;
-
-    case SEEK_CUR:
-        newpos = (long)f->pos + (long)pos;
-        break;
-
-    case SEEK_END:
-        newpos = (long)f->size -  (long)pos;
-        break;
-
-    default:
-        return -1;
-        break;
-  }
-
-  if(newpos < 0) { newpos = 0; }
-  if(newpos > f->size) { newpos = f->size; }
-
-  f->pos = newpos;
-  return newpos;
-}
-
-static int close_mem(void *data) {
-    mem_file* f = (mem_file*)data;
-    free(f);
-    return 0;
-}
-
-static FILE* fmemopen(const char* buffer, size_t size, const char* mode){
-    mem_file* f = (mem_file*)calloc(sizeof(mem_file), 1);
-    if(!f) return NULL;
-
-    f->buffer = buffer;
-    f->size = size;
-
-    return funopen(f, &read_mem, &write_mem, &seek_mem, &close_mem);
-}
-
-#elif defined(ECCODES_ON_WINDOWS)
-
-#include <io.h>
-#include <fcntl.h>
-#include <windows.h>
-
-static FILE *fmemopen(void* buffer, size_t size, const char* mode) {
-    char path[MAX_PATH - 13];
-    if (!GetTempPath(sizeof(path), path))
-        return NULL;
-
-    char filename[MAX_PATH + 1];
-    if (!GetTempFileName(path, "eccodes", 0, filename))
-        return NULL;
-
-    HANDLE h = CreateFile(filename,
-                          GENERIC_READ | GENERIC_WRITE,
-                          0,
-                          NULL,
-                          OPEN_ALWAYS,
-                          FILE_ATTRIBUTE_TEMPORARY | FILE_FLAG_DELETE_ON_CLOSE,
-                          NULL);
-
-    if (h == INVALID_HANDLE_VALUE)
-        return NULL;
-
-    int fd = _open_osfhandle((intptr_t)h, _O_RDWR);
-    if (fd < 0) {
-        CloseHandle(h);
-        return NULL;
-    }
-
-    FILE* f = _fdopen(fd, "w+");
-    if (!f) {
-        _close(fd);
-        return NULL;
-    }
-
-    fwrite(buffer, size, 1, f);
-    rewind(f);
-    return f;
-}
-
-#endif
-
-static size_t entries_count = sizeof(entries)/sizeof(entries[0]);
-
-static const unsigned char* find(const char* path, size_t* length) {
-    size_t i;
-
-    for(i = 0; i < entries_count; i++) {
-        if(strcmp(path, entries[i].path) == 0) {
-            /*printf("Found in MEMFS %s\\n", path);*/
-            *length = entries[i].length;
-            return entries[i].content;
-        }
-    }
-
-    return NULL;
-}
-
-int codes_memfs_exists(const char* path) {
-    size_t dummy;
-    return find(path, &dummy) != NULL;
-}
-
-FILE* codes_memfs_open(const char* path) {
-    size_t size;
-    const unsigned char* mem = find(path, &size);
-    if(!mem) {
-        return NULL;
-    }
-    return fmemopen((void*)mem, size, "r");
-}
-
-""",
-    file=g,
-)
 
 print("Finished")