diff --git a/system/extras/prebuild.sh b/system/extras/prebuild.sh
index 91f878c66f..465d86037a 100755
--- a/system/extras/prebuild.sh
+++ b/system/extras/prebuild.sh
@@ -9,20 +9,37 @@ if [ ! -f "$BUILD_PATH/sketch" ]; then
   mkdir -p "$BUILD_PATH/sketch"
 fi
 
-# Create empty build.opt if build_opt.h does not exists in the original sketch dir
-# Then add or append -fmacro-prefix-map option to change __FILE__ absolute path of
-# the board platform folder to a relative path by using '.'.
-# (i.e. the folder containing boards.txt)
+# Create empty build.opt or clear it if build_opt.h does not exists in the original sketch dir
 if [ ! -f "$BUILD_SOURCE_PATH/build_opt.h" ]; then
-  printf '\n-fmacro-prefix-map="%s"=.' "${BOARD_PLATFORM_PATH//\\/\\\\}" > "$BUILD_PATH/sketch/build.opt"
+  true >"$BUILD_PATH/sketch/build.opt"
 else
   # Else copy the build_opt.h as build.opt
   # Workaround to the header file preprocessing done by arduino-cli
   # See https://github.com/arduino/arduino-cli/issues/1338
-  cp "$BUILD_SOURCE_PATH/build_opt.h" "$BUILD_PATH/sketch/build.opt"
-  printf '\n-fmacro-prefix-map="%s"=.' "${BOARD_PLATFORM_PATH//\\/\\\\}" >> "$BUILD_PATH/sketch/build.opt"
+  cp -f "$BUILD_SOURCE_PATH/build_opt.h" "$BUILD_PATH/sketch/build.opt"
 fi
+# Then append -fmacro-prefix-map option to change __FILE__ absolute path of
+# the board platform folder to a relative path by using '.'.
+# (i.e. the folder containing boards.txt)
+UNAME_OS="$(uname -s)"
+case "${UNAME_OS}" in
+  Windows*)
+    i=0
+    prefix=""
+    while [ "$i" -le "${#BOARD_PLATFORM_PATH}" ]; do
+      prefix=${prefix}${BOARD_PLATFORM_PATH:$i:1}
+      if [ "${BOARD_PLATFORM_PATH:$i:1}" == "\\" ]; then
+        prefix=${prefix}"\\"
+      fi
+      i="$((i + 1))"
+    done
+    ;;
+  *)
+    prefix=${BOARD_PLATFORM_PATH}
+    ;;
+esac
 
+printf '\n-fmacro-prefix-map="%s"=.' "${prefix}" >>"$BUILD_PATH/sketch/build.opt"
 
 # Force include of SrcWrapper library
-echo "#include <SrcWrapper.h>" > "$BUILD_PATH/sketch/SrcWrapper.cpp"
+echo "#include <SrcWrapper.h>" >"$BUILD_PATH/sketch/SrcWrapper.cpp"