Fix a trivial typo.
diff --git a/Python/ast.c b/Python/ast.c
index c1c3907..8b356fe 100644
--- a/Python/ast.c
+++ b/Python/ast.c
@@ -511,7 +511,7 @@
 /* Data structure used internally */
 struct compiling {
     char *c_encoding; /* source encoding */
-    PyArena *c_arena; /* arena for allocating memeory */
+    PyArena *c_arena; /* Arena for allocating memory. */
     PyObject *c_filename; /* filename */
     PyObject *c_normalize; /* Normalization function from unicodedata. */
     PyObject *c_normalize_args; /* Normalization argument tuple. */