diff --git a/win32select.c b/win32select.c
index 68f7697a..a50a2df7 100644
--- a/win32select.c
+++ b/win32select.c
@@ -381,7 +381,7 @@ win32_dealloc(struct event_base *base)
 		mm_free(win32op->exset_out);
 	/* XXXXX free the tree. */
 
-	memset(win32op, 0, sizeof(win32op));
+	memset(win32op, 0, sizeof(*win32op));
 	mm_free(win32op);
 }