Fix typo “a Rc” → “an Rc” (#1191)

1 files changed, 1 insertions, 1 deletions

diff --git a/src/doc/rustc-dev-guide/src/query.md b/src/doc/rustc-dev-guide/src/query.md
index 24b0454b9ab..7195687919d 100644
--- a/src/doc/rustc-dev-guide/src/query.md
+++ b/src/doc/rustc-dev-guide/src/query.md
@@ -60,7 +60,7 @@ method. The answer is that, for each query, the compiler maintains a
 cache – if your query has already been executed, then, the answer is
 simple: we clone the return value out of the cache and return it
 (therefore, you should try to ensure that the return types of queries
-are cheaply cloneable; insert a `Rc` if necessary).
+are cheaply cloneable; insert an `Rc` if necessary).
 
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