diff --git a/builder/main.py b/builder/main.py
index 4d7bbf8..9830f95 100644
--- a/builder/main.py
+++ b/builder/main.py
@@ -95,6 +95,10 @@ def _update_max_upload_size(env):
         env.BoardConfig().update("upload.maximum_size", max(sizes))
 
 
+def _to_unix_slashes(path):
+    return path.replace('\\', '/')
+
+
 #
 # SPIFFS helpers
 #
@@ -317,11 +321,13 @@ elif upload_protocol in debug_tools:
     uploader_flags.extend(["-c", 'program_esp32 "{{$SOURCE}}" 0x10000 verify'])
     for image in env.get("FLASH_EXTRA_IMAGES", []):
         uploader_flags.extend(
-            ["-c", 'program_esp32 "%s" %s verify' % (image[1].replace('\\', '/'), image[0].replace('\\', '/'))])
+            ["-c", 'program_esp32 "{{%s}}" %s verify' % (
+                _to_unix_slashes(image[1]), _to_unix_slashes(image[0]))])
     uploader_flags.extend(["-c", "reset run; shutdown"])
     for i, item in enumerate(uploader_flags):
         if "$PACKAGE_DIR" in item:
-            uploader_flags[i] = item.replace("$PACKAGE_DIR", openocd_dir.replace('\\', '/'))
+            uploader_flags[i] = item.replace(
+                "$PACKAGE_DIR", _to_unix_slashes(openocd_dir))
 
     env.Replace(
         UPLOADER="openocd",