diff --git a/Python/pythonrun.c b/Python/pythonrun.c
index 5891d50cd3f..f9daf8168f1 100644
--- a/Python/pythonrun.c
+++ b/Python/pythonrun.c
@@ -1485,6 +1485,7 @@ Py_CompileStringObject(const char *str, PyObject *filename, int start,
     if (flags && (flags->cf_flags & PyCF_ONLY_AST)) {
         if ((flags->cf_flags & PyCF_OPTIMIZED_AST) == PyCF_OPTIMIZED_AST) {
             if (_PyCompile_AstOptimize(mod, filename, flags, optimize, arena) < 0) {
+                _PyArena_Free(arena);
                 return NULL;
             }
         }