diff --git a/Lib/fontmake/font_project.py b/Lib/fontmake/font_project.py
index 3e3ee365..3f654011 100644
--- a/Lib/fontmake/font_project.py
+++ b/Lib/fontmake/font_project.py
@@ -547,7 +547,7 @@ def _designspace_locations(self, designspace_path):
 
         maps = []
         ds = varLib.designspace.load(designspace_path)
-        for location_list in (ds['sources'], ds['instances']):
+        for location_list in (ds['sources'], ds.get('instances', [])):
             location_map = {}
             for loc in location_list:
                 abspath = os.path.normpath(os.path.join(