diff --git a/radio/util/Dockerfile b/radio/util/Dockerfile
index 315acb3bd..7648b0302 100644
--- a/radio/util/Dockerfile
+++ b/radio/util/Dockerfile
@@ -23,3 +23,5 @@ ENV PATH $PATH:/opt/gcc-arm-none-eabi/bin:/opentx/code/radio/util
 
 ARG OPENTX_VERSION_SUFFIX=
 ENV OPENTX_VERSION_SUFFIX ${OPENTX_VERSION_SUFFIX}
+
+WORKDIR /build
diff --git a/radio/util/build-firmware.py b/radio/util/build-firmware.py
index efd057d65..7b5e3ecce 100755
--- a/radio/util/build-firmware.py
+++ b/radio/util/build-firmware.py
@@ -16,11 +16,6 @@ INVALID_FIRMWARE = 5
 INVALID_BOARD = 6
 INVALID_LANGUAGE = 7
 
-# Board types
-BOARD_SKY9X = 2
-BOARD_TARANIS = 3
-BOARD_HORUS = 4
-
 
 def build_target(target, path, cmake_options):
     srcdir = os.path.dirname(os.path.realpath(__file__)) + "/../.."
@@ -56,183 +51,180 @@ def build_target(target, path, cmake_options):
         open(errpath, "w").write(output.decode("utf-8") + error.decode("utf-8"))
         return COMPILATION_ERROR
 
+    return 0
+
+
+def main():
+    if len(sys.argv) != 3:
+        exit(INVALID_FIRMWARE)
+
+    target = sys.argv[1]
+    directory, filename = os.path.split(sys.argv[2])
+    root, ext = os.path.splitext(filename)
+    options = root.split("-")
+
+    if len(options) < 2 or options[0] != "opentx":
+        exit(INVALID_FIRMWARE)
+
+    optcount = 1
+    cmake_options = {}
+    board_name = options[optcount]
+
+    if board_name == "sky9x":
+        cmake_options["PCB"] = "SKY9X"
+        firmware_options = options_sky9x
+        maxsize = 65536 * 4
+    elif board_name == "9xrpro":
+        cmake_options["PCB"] = "9XRPRO"
+        cmake_options["SDCARD"] = "YES"
+        firmware_options = options_sky9x
+        maxsize = 65536 * 4
+    elif board_name == "ar9x":
+        cmake_options["PCB"] = "AR9X"
+        cmake_options["SDCARD"] = "YES"
+        firmware_options = options_ar9x
+        maxsize = 65536 * 4
+    elif board_name == "x9lite":
+        cmake_options["PCB"] = "X9LITE"
+        cmake_options["MULTI_SPORT"] = "ON"
+        firmware_options = options_taranis_x9lite
+        maxsize = 65536 * 8
+    elif board_name == "x7":
+        cmake_options["PCB"] = "X7"
+        cmake_options["MULTI_SPORT"] = "ON"
+        firmware_options = options_taranis_x9dp
+        maxsize = 65536 * 8
+    elif board_name == "xlite":
+        cmake_options["PCB"] = "XLITE"
+        cmake_options["MULTI_SPORT"] = "ON"
+        firmware_options = options_taranis_xlite
+        maxsize = 65536 * 8
+    elif board_name == "xlites":
+        cmake_options["PCB"] = "XLITES"
+        cmake_options["MULTI_SPORT"] = "ON"
+        firmware_options = options_taranis_xlites
+        maxsize = 65536 * 8
+    elif board_name == "x9d":
+        cmake_options["PCB"] = "X9D"
+        cmake_options["MULTI_SPORT"] = "ON"
+        firmware_options = options_taranis_x9d
+        maxsize = 65536 * 8
+    elif board_name == "x9d+":
+        cmake_options["PCB"] = "X9D+"
+        cmake_options["MULTI_SPORT"] = "ON"
+        firmware_options = options_taranis_x9dp
+        maxsize = 65536 * 8
+    elif board_name == "x9d+2019":
+        cmake_options["PCB"] = "X9D+"
+        cmake_options["PCBREV"] = "2019"
+        cmake_options["MULTI_SPORT"] = "ON"
+        firmware_options = options_taranis_x9dp
+        maxsize = 65536 * 8
+    elif board_name == "x9e":
+        cmake_options["PCB"] = "X9E"
+        cmake_options["MULTI_SPORT"] = "ON"
+        firmware_options = options_taranis_x9e
+        maxsize = 65536 * 8
+    elif board_name == "x10":
+        cmake_options["PCB"] = "X10"
+        cmake_options["MULTI_SPORT"] = "ON"
+        firmware_options = options_horus_x10
+        maxsize = 2 * 1024 * 1024
+    elif board_name == "x12s":
+        cmake_options["PCB"] = "X12S"
+        cmake_options["MULTI_SPORT"] = "ON"
+        firmware_options = options_horus_x12s
+        maxsize = 2 * 1024 * 1024
+    elif board_name == "t12":
+        cmake_options["PCB"] = "X7"
+        cmake_options["PCBREV"] = "T12"
+        cmake_options["MULTI_SPORT"] = "ON"
+        firmware_options = options_taranis_x9dp
+        maxsize = 65536 * 8
+    else:
+        exit(INVALID_BOARD)
+
+    if target == "firmware":
+        binary = "firmware.bin"
+        ext = ".bin"
+        filename = "opentx"
+    elif target == "libsimulator":
+        binary = "libopentx-" + board_name + "-simulator.so"
+        ext = ".so"
+        filename = "libopentx"
+    else:
+        exit(INVALID_BOARD)
+
+    filename += "-" + board_name
+    optcount += 1
+
+    # The firmware options
+    for opt, values in firmware_options.items():
+        found = False
+        for i in range(optcount, len(options)):
+            if options[i] == opt:
+                found = True
+                break
+
+        if not isinstance(values, list):
+            values = [values]
+
+        for name, value1, value2 in values:
+            if found:
+                value = value1
+                filename += "-" + opt
+            else:
+                value = value2
+
+            if value is not None:
+                cmake_options[name] = value
+
+    # The firmware display language
+    language = ""
+    for key in languages:
+        if key == options[-1]:
+            language = key
+    if not language:
+        exit(INVALID_LANGUAGE)
+    cmake_options["TRANSLATIONS"] = language.upper()
+
+    filename += "-" + language + ext
+    path = os.path.join(directory, filename)
+    errpath = path + ".err"
+
+    if os.path.isfile(errpath):
+        print(filename)
+        exit(COMPILATION_ERROR)
+
+    if os.path.isfile(path):
+        print(filename)
+        exit(0)
+
+    lockpath = path + ".lock"
+    lock = filelock.FileLock(lockpath)
+    try:
+        with lock.acquire(timeout=60 * 60):
+            if not os.path.isfile(path):
+                result = build_target(target, path, cmake_options)
+                if result != 0:
+                    print(filename)
+                    return result
+    except filelock.Timeout:
+        print(filename)
+        exit(COMPILATION_ERROR)
+
     if target == "firmware":
         # Check binary size
-        size = os.stat(target).st_size
+        size = os.stat(binary).st_size
         if size > maxsize:
             return FIRMWARE_SIZE_TOO_BIG
 
     # Copy binary to the binaries directory
-    shutil.move(target, path)
+    shutil.move(binary, path)
 
-if len(sys.argv) != 3:
-    exit(INVALID_FIRMWARE)
-
-target = sys.argv[1]
-directory, filename = os.path.split(sys.argv[2])
-root, ext = os.path.splitext(filename)
-options = root.split("-")
-
-if len(options) < 2 or options[0] != "opentx":
-    exit(INVALID_FIRMWARE)
-
-optcount = 1
-cmake_options = {}
-
-
-if options[optcount] == "sky9x":
-    cmake_options["PCB"] = "SKY9X"
-    firmware_options = options_sky9x
-    maxsize = 65536 * 4
-    board = BOARD_SKY9X
-elif options[optcount] == "9xrpro":
-    cmake_options["PCB"] = "9XRPRO"
-    cmake_options["SDCARD"] = "YES"
-    firmware_options = options_sky9x
-    maxsize = 65536 * 4
-    board = BOARD_SKY9X
-elif options[optcount] == "ar9x":
-    cmake_options["PCB"] = "AR9X"
-    cmake_options["SDCARD"] = "YES"
-    firmware_options = options_ar9x
-    maxsize = 65536 * 4
-    board = BOARD_SKY9X
-elif options[optcount] == "x9lite":
-    cmake_options["PCB"] = "X9LITE"
-    cmake_options["MULTI_SPORT"] = "ON"
-    firmware_options = options_taranis_x9lite
-    maxsize = 65536 * 8
-    board = BOARD_TARANIS
-elif options[optcount] == "x7":
-    cmake_options["PCB"] = "X7"
-    cmake_options["MULTI_SPORT"] = "ON"
-    firmware_options = options_taranis_x9dp
-    maxsize = 65536 * 8
-    board = BOARD_TARANIS
-elif options[optcount] == "xlite":
-    cmake_options["PCB"] = "XLITE"
-    cmake_options["MULTI_SPORT"] = "ON"
-    firmware_options = options_taranis_xlite
-    maxsize = 65536 * 8
-    board = BOARD_TARANIS
-elif options[optcount] == "xlites":
-    cmake_options["PCB"] = "XLITES"
-    cmake_options["MULTI_SPORT"] = "ON"
-    firmware_options = options_taranis_xlites
-    maxsize = 65536 * 8
-    board = BOARD_TARANIS
-elif options[optcount] == "x9d":
-    cmake_options["PCB"] = "X9D"
-    cmake_options["MULTI_SPORT"] = "ON"
-    firmware_options = options_taranis_x9d
-    maxsize = 65536 * 8
-    board = BOARD_TARANIS
-elif options[optcount] == "x9d+":
-    cmake_options["PCB"] = "X9D+"
-    cmake_options["MULTI_SPORT"] = "ON"
-    firmware_options = options_taranis_x9dp
-    maxsize = 65536 * 8
-    board = BOARD_TARANIS
-elif options[optcount] == "x9d+2019":
-    cmake_options["PCB"] = "X9D+"
-    cmake_options["PCBREV"] = "2019"
-    cmake_options["MULTI_SPORT"] = "ON"
-    firmware_options = options_taranis_x9dp
-    maxsize = 65536 * 8
-    board = BOARD_TARANIS
-elif options[optcount] == "x9e":
-    cmake_options["PCB"] = "X9E"
-    cmake_options["MULTI_SPORT"] = "ON"
-    firmware_options = options_taranis_x9e
-    maxsize = 65536 * 8
-    board = BOARD_TARANIS
-elif options[optcount] == "x10":
-    cmake_options["PCB"] = "X10"
-    cmake_options["MULTI_SPORT"] = "ON"
-    firmware_options = options_horus_x10
-    maxsize = 2 * 1024 * 1024
-    board = BOARD_HORUS
-elif options[optcount] == "x12s":
-    cmake_options["PCB"] = "X12S"
-    cmake_options["MULTI_SPORT"] = "ON"
-    firmware_options = options_horus_x12s
-    maxsize = 2 * 1024 * 1024
-    board = BOARD_HORUS
-elif options[optcount] == "t12":
-    cmake_options["PCB"] = "X7"
-    cmake_options["PCBREV"] = "T12"
-    cmake_options["MULTI_SPORT"] = "ON"
-    firmware_options = options_taranis_x9dp
-    maxsize = 65536 * 8
-    board = BOARD_TARANIS
-else:
-    exit(INVALID_BOARD)
-
-if target == "firmware":
-    ext = ".bin"
-    target = "firmware" + ext
-    filename = "opentx"
-elif target == "libsimulator":
-    ext = ".so"
-    target = "libopentx-" + options[optcount] + "-simulator.so"
-    filename = "libopentx"
-else:
-    exit(INVALID_BOARD)
-
-filename += "-" + options[optcount]
-optcount += 1
-
-# The firmware options
-for opt, values in firmware_options.items():
-    found = False
-    for i in range(optcount, len(options)):
-        if options[i] == opt:
-            found = True
-            break
-
-    if not isinstance(values, list):
-        values = [values]
-
-    for name, value1, value2 in values:
-        if found:
-            value = value1
-            filename += "-" + opt
-        else:
-            value = value2
-
-        if value is not None:
-            cmake_options[name] = value
-
-# The firmware display language
-language = ""
-for key in languages:
-    if key == options[-1]:
-        language = key
-if not language:
-    exit(INVALID_LANGUAGE)
-cmake_options["TRANSLATIONS"] = language.upper()
-
-filename += "-" + language + ext
-path = os.path.join(directory, filename)
-errpath = path + ".err"
-
-if os.path.isfile(errpath):
-    print(filename)
-    exit(COMPILATION_ERROR)
-
-if os.path.isfile(path):
     print(filename)
     exit(0)
 
-lockpath = path + ".lock"
-lock = filelock.FileLock(lockpath)
-try:
-    with lock.acquire(timeout = 60*60):
-        if not os.path.isfile(path):
-            build_target(target, path)
-except filelock.Timeout:
-    print(filename)
-    exit(COMPILATION_ERROR)
 
-print(filename)
-exit(0)
+if __name__ == "__main__":
+    main()