diff --git a/reactos/tools/fatten/fatfs/diskio.c b/reactos/tools/fatten/fatfs/diskio.c
index c77dd2084f2..98d2aee57f0 100644
--- a/reactos/tools/fatten/fatfs/diskio.c
+++ b/reactos/tools/fatten/fatfs/diskio.c
@@ -30,7 +30,7 @@ DSTATUS disk_openimage(BYTE pdrv, const char* imageFileName)
         driveHandle[0] = fopen(imageFileName, "r+b");
         if (!driveHandle[0])
         {
-            driveHandle[0] = fopen(imageFileName, "w+");
+            driveHandle[0] = fopen(imageFileName, "w+b");
         }
 
         if (driveHandle[0] != NULL)
diff --git a/reactos/tools/fatten/fatten.c b/reactos/tools/fatten/fatten.c
index 429e2244c33..9e07172b944 100644
--- a/reactos/tools/fatten/fatten.c
+++ b/reactos/tools/fatten/fatten.c
@@ -232,8 +232,10 @@ int main(int oargc, char* oargv[])
             }
             else
             {
-                // Quick&dirty hardcoded length.
-                memcpy(buff + 2, temp + 2, 0x3E - 0x02);
+#define FAT16_HEADER_START 3
+#define FAT16_HEADER_END 62
+
+                memcpy(buff + FAT16_HEADER_START, temp + FAT16_HEADER_START, FAT16_HEADER_END - FAT16_HEADER_START);
             }
 
             if (disk_write(0, buff, 0, 1))