diff --git a/reactos/boot/freeldr/bootsect/CMakeLists.txt b/reactos/boot/freeldr/bootsect/CMakeLists.txt
index 1a268a7176b..f76ac7a95bb 100644
--- a/reactos/boot/freeldr/bootsect/CMakeLists.txt
+++ b/reactos/boot/freeldr/bootsect/CMakeLists.txt
@@ -20,6 +20,7 @@ if(ARCH STREQUAL "i386" OR ARCH STREQUAL "amd64")
 
     CreateBootSectorTarget(isoboot ${CMAKE_CURRENT_SOURCE_DIR}/isoboot.S ${CMAKE_CURRENT_BINARY_DIR}/isoboot.bin 7000)
     CreateBootSectorTarget(isobtrt ${CMAKE_CURRENT_SOURCE_DIR}/isobtrt.S ${CMAKE_CURRENT_BINARY_DIR}/isobtrt.bin 7000)
+    CreateBootSectorTarget(isombr ${CMAKE_CURRENT_SOURCE_DIR}/isombr.S ${CMAKE_CURRENT_BINARY_DIR}/isombr.bin 7000)
 
     add_cd_file(TARGET dosmbr DESTINATION loader NO_CAB FILE ${CMAKE_CURRENT_BINARY_DIR}/dosmbr.bin FOR bootcd regtest)
     add_cd_file(TARGET ext2 DESTINATION loader NO_CAB FILE ${CMAKE_CURRENT_BINARY_DIR}/ext2.bin FOR bootcd regtest)
diff --git a/reactos/boot/freeldr/bootsect/isombr.S b/reactos/boot/freeldr/bootsect/isombr.S
new file mode 100644
index 00000000000..93da60718a7
--- /dev/null
+++ b/reactos/boot/freeldr/bootsect/isombr.S
@@ -0,0 +1,102 @@
+/*
+ * PROJECT:     ReactOS MBR Boot Sector for ISO file system ("isohybrid mode")
+ * LICENSE:     GNU GPLv2 or any later version as published by the Free Software Foundation
+ * COPYRIGHT:   Copyright 2017 Colin Finck <colin@reactos.org>
+ */
+
+#include <asm.inc>
+
+.code16
+
+// The "isohybrid" tool patching our ISO will write the LBA of the El Torito BIOS Boot Sector to this address.
+pBootSectorLBA = start+432;
+
+// Our BIOS Boot Sector contains this signature at the specified position and our third-party imported "isohybrid" patching tool checks for it.
+// This is also why it's the same signature ISOLINUX uses.
+HybridSignature = HEX(7078C0FB)
+pBootSectorHybridSignature = HEX(7C00)+64
+pBootSectorHybridEntryPoint = HEX(7C00)+64+4
+
+start:
+    // The MBR needs to start with 33h, because some dumb BIOSes check for that (cf. syslinux commit d0f275981c9289dc4b8df64e72cd9902bf85aebe).
+    // The following line encodes a "xor ax, ax" (but it's not the only way to encode it, so we can't just write that instruction here).
+    .byte HEX(33), HEX(C0)
+
+    // Set up our stack and a flat addressing model.
+    cli
+    mov ss, ax
+    mov sp, offset start
+    mov ds, ax
+    mov es, ax
+    mov fs, ax
+    mov gs, ax
+    sti
+
+    // Our boot sector has been loaded to address 0x7C00.
+    // Relocate our 512 bytes boot sector to the given base address (should be 0x7000).
+    cld
+    mov cx, 512 / 4
+    mov si, HEX(7C00)
+    mov di, offset start
+    rep movsd
+
+    // Jump to the relocated code.
+    ljmp16 0, relocated
+
+relocated:
+    // Prepare the Disk Access Packet (DAP) for INT 13h, Function 42h: Extended Read Sectors from Drive.
+    // Read 4 sectors to address 7C00h, which is exactly our 2K-sized BIOS Boot Sector.
+    push 0
+    push 0
+    push dword ptr es:[pBootSectorLBA]
+    push es
+    push HEX(7C00)
+    push 4
+    push HEX(10)
+
+    // Call the BIOS function. Note that we haven't clobbered DL up to this point, so the Drive Number passed by the BIOS is still there.
+    // Read errors are indicated by the Carry Flag.
+    mov ah, HEX(42)
+    mov si, sp
+    int HEX(13)
+    jc read_error
+
+    // Verify the Hybrid Signature.
+    cmp dword ptr es:[pBootSectorHybridSignature], HybridSignature
+    jne invalid_signature
+
+    // Signature is valid, so jump to the entry point for the hybrid code.
+    ljmp16 0, pBootSectorHybridEntryPoint
+
+read_error:
+    call die_with_error
+    .ascii "ISOMBR: Read Error!", CR, LF
+
+invalid_signature:
+    call die_with_error
+    .ascii "ISOMBR: Invalid Boot Sector Hybrid Signature!", CR, LF
+
+die_with_error:
+    // Fetch the message to output stored at the return address on the stack.
+    pop si
+
+    // Call BIOS INT 10h, Function 0Eh to output a single character.
+    // Do this in a loop and stop after we have printed the newline LF character.
+next_character:
+    lodsb
+    mov ah, HEX(0E)
+    xor bx, bx
+    int HEX(10)
+    cmp al, 10
+    jne next_character
+
+    // Die gracefully, that means in an infinite HLT loop to not put any stress on the CPU.
+die:
+    hlt
+    jmp die
+
+// The "isohybrid" tool will add the remaining information, including the infamous 0xAA55 MBR signature.
+
+.endcode16
+
+END