diff --git a/AMBuildScript b/AMBuildScript
index db22453..40fdc01 100644
--- a/AMBuildScript
+++ b/AMBuildScript
@@ -157,6 +157,8 @@ class MMSConfig(object):
       if sdk.shouldBuild(self.all_targets):
         if builder.options.hl2sdk_root:
           sdk_path = os.path.join(builder.options.hl2sdk_root, sdk.folder)
+          if not os.path.exists(sdk_path):
+            sdk_path = None
         else:
           sdk_path = ResolveEnvPath(sdk.envvar, sdk.folder)
         if sdk_path is None: