diff --git a/desktop_version/src/FileSystemUtils.cpp b/desktop_version/src/FileSystemUtils.cpp
index 1160f63f..419cf834 100644
--- a/desktop_version/src/FileSystemUtils.cpp
+++ b/desktop_version/src/FileSystemUtils.cpp
@@ -11,6 +11,7 @@
 #include "Exit.h"
 #include "Graphics.h"
 #include "Maths.h"
+#include "Unused.h"
 #include "UtilityClass.h"
 
 /* These are needed for PLATFORM_* crap */
@@ -309,10 +310,148 @@ static bool FILESYSTEM_mountAssetsFrom(const char *fname)
 	return true;
 }
 
+struct ArchiveState
+{
+	const char* filename;
+	bool has_extension;
+	bool other_level_files;
+};
+
+static PHYSFS_EnumerateCallbackResult zipCheckCallback(
+	void* data,
+	const char* origdir,
+	const char* filename
+) {
+	struct ArchiveState* state = (struct ArchiveState*) data;
+	const bool has_extension = endsWith(filename, ".vvvvvv");
+	UNUSED(origdir);
+
+	if (!state->has_extension)
+	{
+		state->has_extension = has_extension;
+	}
+	if (!state->other_level_files && has_extension)
+	{
+		state->other_level_files = SDL_strcmp(
+			state->filename,
+			filename
+		) != 0;
+	}
+
+	if (state->has_extension && state->other_level_files)
+	{
+		/* We don't need to check any more files. */
+		return PHYSFS_ENUM_STOP;
+	}
+	return PHYSFS_ENUM_OK;
+}
+
+/* For technical reasons, the level file inside a zip named LEVELNAME.zip must
+ * be named LEVELNAME.vvvvvv, else its custom assets won't work;
+ * if there are .vvvvvv files other than LEVELNAME.vvvvvv, they would be loaded
+ * too but they won't load any assets
+ *
+ * For user-friendliness, we check this upfront and reject all zips that don't
+ * conform to this (regardless of them containing assets or not) - otherwise a
+ * level zip with assets can be played but its assets mysteriously won't work
+ */
+static bool checkZipStructure(const char* filename)
+{
+	const char* real_dir = PHYSFS_getRealDir(filename);
+	char base_name[MAX_PATH];
+	char real_path[MAX_PATH];
+	char mount_path[MAX_PATH];
+	char check_path[MAX_PATH];
+	char random_str[6 + 1];
+	bool success;
+	struct ArchiveState zip_state;
+
+	if (real_dir == NULL)
+	{
+		printf(
+			"Could not check %s: real directory doesn't exist\n",
+			filename
+		);
+		return false;
+	}
+
+	SDL_snprintf(real_path, sizeof(real_path), "%s/%s", real_dir, filename);
+
+	generateBase36(random_str, sizeof(random_str));
+	SDL_snprintf(mount_path, sizeof(mount_path), ".vvv-mnt-temp-%s/", random_str);
+
+	if (!PHYSFS_mount(real_path, mount_path, 1))
+	{
+		printf(
+			"Error mounting and checking %s: %s\n",
+			filename,
+			PHYSFS_getErrorByCode(PHYSFS_getLastErrorCode())
+		);
+		return false;
+	}
+
+	VVV_between(filename, "levels/", base_name, ".zip");
+
+	SDL_snprintf(
+		check_path,
+		sizeof(check_path),
+		"%s%s.vvvvvv",
+		mount_path,
+		base_name
+	);
+
+	success = PHYSFS_exists(check_path);
+
+	SDL_zero(zip_state);
+	zip_state.filename = check_path;
+
+	PHYSFS_enumerate(mount_path, zipCheckCallback, (void*) &zip_state);
+
+	/* If no .vvvvvv files in zip, don't print warning. */
+	if (!success && zip_state.has_extension)
+	{
+		/* FIXME: How do we print this for non-terminal users? */
+		printf(
+			"%s.zip is not structured correctly! It is missing %s.vvvvvv.\n",
+			base_name,
+			base_name
+		);
+	}
+
+	success &= !zip_state.other_level_files;
+
+	/* ...But if other .vvvvvv file(s), do print warning. */
+	if (zip_state.other_level_files)
+	{
+		/* FIXME: How do we print this for non-terminal users? */
+		printf(
+			"%s.zip is not structured correctly! It has .vvvvvv file(s) other than %s.vvvvvv.\n",
+			base_name,
+			base_name
+		);
+	}
+
+	if (!PHYSFS_unmount(real_path))
+	{
+		printf(
+			"Could not unmount %s: %s\n",
+			mount_path,
+			PHYSFS_getErrorByCode(PHYSFS_getLastErrorCode())
+		);
+	}
+
+	return success;
+}
+
 void FILESYSTEM_loadZip(const char* filename)
 {
 	PHYSFS_File* zip = PHYSFS_openRead(filename);
 
+	if (!checkZipStructure(filename))
+	{
+		return;
+	}
+
 	if (!PHYSFS_mountHandle(zip, filename, "levels", 1))
 	{
 		printf(