Add missing "a".
diff --git a/Doc/howto/doanddont.rst b/Doc/howto/doanddont.rst
index 2e9e0b8..15aa996 100644
--- a/Doc/howto/doanddont.rst
+++ b/Doc/howto/doanddont.rst
@@ -113,7 +113,7 @@
This is a "don't" which is much weaker than the previous "don't"s but is still
something you should not do if you don't have good reasons to do that. The
-reason it is usually bad idea is because you suddenly have an object which lives
+reason it is usually a bad idea is because you suddenly have an object which lives
in two separate namespaces. When the binding in one namespace changes, the
binding in the other will not, so there will be a discrepancy between them. This
happens when, for example, one module is reloaded, or changes the definition of