diff --git a/src/bootstrap/bootstrap_test.py b/src/bootstrap/bootstrap_test.py
index 1e46348577d..5ecda83ee66 100644
--- a/src/bootstrap/bootstrap_test.py
+++ b/src/bootstrap/bootstrap_test.py
@@ -117,6 +117,8 @@ class GenerateAndParseConfig(unittest.TestCase):
         self.assertNotEqual(build.config_toml.find("codegen-backends = ['cranelift']"), -1)
         build = self.serialize_and_parse(["--set", "rust.codegen-backends=cranelift,llvm"])
         self.assertNotEqual(build.config_toml.find("codegen-backends = ['cranelift', 'llvm']"), -1)
+        build = self.serialize_and_parse(["--enable-full-tools"])
+        self.assertNotEqual(build.config_toml.find("codegen-backends = ['llvm']"), -1)
 
 if __name__ == '__main__':
     SUITE = unittest.TestSuite()
diff --git a/src/bootstrap/configure.py b/src/bootstrap/configure.py
index c1ea9dd0ce3..571062a3a6f 100755
--- a/src/bootstrap/configure.py
+++ b/src/bootstrap/configure.py
@@ -299,7 +299,7 @@ def set(key, value, config):
     parts = key.split('.')
     for i, part in enumerate(parts):
         if i == len(parts) - 1:
-            if is_value_list(part):
+            if is_value_list(part) and isinstance(value, str):
                 value = value.split(',')
             arr[part] = value
         else: