--- a/build/moz.configure/bootstrap.configure
+++ b/build/moz.configure/bootstrap.configure
@@ -123,16 +123,18 @@ def bootstrap_path(path, **kwargs):
     @imports("os")
     @imports("subprocess")
     @imports("sys")
     @imports(_from="mozbuild.util", _import="ensureParentDir")
     @imports(_from="importlib", _import="import_module")
     @imports(_from="__builtin__", _import="open")
     @imports(_from="__builtin__", _import="Exception")
     def bootstrap_path(bootstrap, toolchains_base_dir, tasks, build_env, path):
+        if not path:
+            return
         path_parts = path.split("/")
 
         def try_bootstrap(exists):
             if not tasks:
                 return False
             prefixes = [""]
             if tasks.prefix:
                 prefixes.insert(0, "{}-".format(tasks.prefix))

--- a/build/moz.configure/pkg.configure
+++ b/build/moz.configure/pkg.configure
@@ -8,17 +8,17 @@
 @depends(toolchain_prefix, when=compile_environment)
 def pkg_config(prefixes):
     return tuple("{}pkg-config".format(p) for p in (prefixes or ()) + ("",))
 
 
 pkg_config = check_prog(
     "PKG_CONFIG",
     pkg_config,
-    bootstrap="pkgconf",
+    bootstrap=depends(when=target_sysroot.bootstrapped)(lambda: "pkgconf"),
     allow_missing=True,
     when=compile_environment
     & depends(target.os)(lambda os: os not in ("WINNT", "OSX", "Android")),
 )
 
 
 @depends_if(pkg_config)
 @checking("for pkg-config version")