diff --git a/conda_build/metadata.py b/conda_build/metadata.py
index 37e94367d4..4681fd653c 100644
--- a/conda_build/metadata.py
+++ b/conda_build/metadata.py
@@ -2668,13 +2668,11 @@ def get_loop_vars(self):
         return variants.get_vars(_variants, loop_only=True)
 
     def get_used_loop_vars(self, force_top_level=False, force_global=False):
-        return {
-            var
-            for var in self.get_used_vars(
-                force_top_level=force_top_level, force_global=force_global
-            )
-            if var in self.get_loop_vars()
-        }
+        loop_vars = self.get_loop_vars()
+        used_vars = self.get_used_vars(
+            force_top_level=force_top_level, force_global=force_global
+        )
+        return set(loop_vars).intersection(used_vars)
 
     def get_rendered_recipe_text(
         self, permit_undefined_jinja=False, extract_pattern=None
diff --git a/conda_build/variants.py b/conda_build/variants.py
index 46862fdbe4..a47c573ef0 100644
--- a/conda_build/variants.py
+++ b/conda_build/variants.py
@@ -697,16 +697,18 @@ def get_package_variants(recipedir_or_metadata, config=None, variants=None):
 def get_vars(variants, loop_only=False):
     """For purposes of naming/identifying, provide a way of identifying which variables contribute
     to the matrix dimensionality"""
-    special_keys = {"pin_run_as_build", "zip_keys", "ignore_version"}
-    special_keys.update(set(ensure_list(variants[0].get("extend_keys"))))
+    first_variant, *other_variants = variants
+    special_keys = {
+        "pin_run_as_build",
+        "zip_keys",
+        "ignore_version",
+        *ensure_list(first_variant.get("extend_keys")),
+    }
     loop_vars = [
         k
-        for k in variants[0]
+        for k, v in first_variant.items()
         if k not in special_keys
-        and (
-            not loop_only
-            or any(variant[k] != variants[0][k] for variant in variants[1:])
-        )
+        and (not loop_only or any(variant[k] != v for variant in other_variants))
     ]
     return loop_vars