diff --git a/pio-tools/post_esp32.py b/pio-tools/post_esp32.py
index 904d24394..bef91e345 100644
--- a/pio-tools/post_esp32.py
+++ b/pio-tools/post_esp32.py
@@ -2,24 +2,91 @@
 # Thanks TD-er :)
 
 Import("env")
+import os
+
+def decode_flash_size_speed(byte_value):
+    speed = byte_value[0] & 0x0f
+    size = (byte_value[0] & 0xf0) / 16
+
+    spi_speed = {
+      0: "40",
+      1: "26",
+      2: "20",
+      0xf: "80"
+    }
+    speed_mhz = spi_speed.get(speed)
+    size_mb = str(1<<int(size))
+
+    return "0x{}: {}MHz, {}MB".format(byte_value.hex(), speed_mhz, size_mb)
+
 
 def esp32_create_factory_bin(source, target, env):
-    #print("Generating one file initial flash firmware for esp32 units")
+    #print("Generating one file initial flash firmware for esp32")
+
     offset = 0x0
+    flash_page_size = 256
+
+    # The offset from begin of the file where the app0 partition starts
+    # This is defined in the partition .csv file
+    sketch_partition_start = 0x10000
+
+    # Typical layout of the generated file:
+    #    Offset | File
+    # -  0x1000 | ~\.platformio\packages\framework-arduinoespressif32\tools\sdk\esp32\bin\bootloader_dout_40m.bin
+    # -  0x8000 | ~\Tasmota\.pio\build\<env name>\partitions.bin
+    # -  0xe000 | ~\.platformio\packages\framework-arduinoespressif32\tools\partitions\boot_app0.bin
+    # - 0x10000 | ~\Tasmota\.pio\build\<env name>/firmware.bin
+
     new_file_name = env.subst("$BUILD_DIR/${PROGNAME}-factory.bin")
     sections = env.subst(env.get('FLASH_EXTRA_IMAGES'))
     new_file = open(new_file_name,"wb")
+    new_file.truncate() # Make sure no left over data is present from a previous build
+
+    firmware_name = env.subst("$BUILD_DIR/${PROGNAME}.bin")
+
+    # fill the file with 0xFF binary data to reflect 'erased and not yet written' data.
+    # Make sure to use exactly the size that normally would be erased
+    new_file.seek(0)
+    total_size = sketch_partition_start + os.path.getsize(firmware_name)
+    total_size = total_size - (total_size % flash_page_size) + flash_page_size
+
+    new_file.write(bytes([0xff] * total_size))
+
     print("    {} | {}".format("Offset", "File"))
     for section in sections:
       sect_adr,sect_file = section.split(" ",1)
       print(" -  {} | {}".format(sect_adr,sect_file))
       source = open(sect_file,"rb")
       new_file.seek(int(sect_adr,0)-offset)
-      new_file.write(source.read());
+      new_file.write(source.read())
+      if "bootloader" in sect_file:
+        # Need to patch the bootloader to match the flash size
+        flash_size = env.BoardConfig().get("upload.flash_size")
+
+        spi_speed_size_byte_offset = 3
+        source.seek(spi_speed_size_byte_offset)
+        spi_speed_size_byte = source.read(1)
+        new_spi_speed_size_byte = spi_speed_size_byte[0] & 0x0f
+
+        spi_size = {
+          "1MB": 0x00,
+          "2MB": 0x10,
+          "4MB": 0x20,
+          "8MB": 0x30,
+          "16MB": 0x40
+        }
+        new_spi_speed_size_byte |= spi_size.get(flash_size, spi_speed_size_byte[0] & 0xf0)
+
+        if new_spi_speed_size_byte != spi_speed_size_byte:
+          new_byte = bytes([new_spi_speed_size_byte])
+          print("           | Patch flash size value {} -> {}".format(decode_flash_size_speed(spi_speed_size_byte), decode_flash_size_speed(new_byte)))
+          new_file.seek(int(sect_adr,0)-offset + spi_speed_size_byte_offset)
+          new_file.write(new_byte)
+
       source.close()
 
-    firmware_name = env.subst("$BUILD_DIR/${PROGNAME}.bin")
-    firmware_start = 0x10000-offset
+
+    firmware_start = sketch_partition_start-offset
     firmware = open(firmware_name,"rb")
     print(" - {} | {}".format(hex(firmware_start),firmware_name))
     new_file.seek(firmware_start)