diff --git a/src/bootstrap/configure.py b/src/bootstrap/configure.py
index 67337bf44214e..176e94355287f 100755
--- a/src/bootstrap/configure.py
+++ b/src/bootstrap/configure.py
@@ -360,7 +360,7 @@ def to_toml(value):
     elif isinstance(value, str):
         return "'" + value + "'"
     else:
-        raise 'no toml'
+        raise RuntimeError('no toml')
 
 def configure_section(lines, config):
     for key in config: