2 files changed, 3 insertions, 2 deletions
diff --git a/qga/vss-win32/requester.cpp b/qga/vss-win32/requester.cpp
index b130fee934..aae0d5f2bf 100644
--- a/qga/vss-win32/requester.cpp
+++ b/qga/vss-win32/requester.cpp
@@ -25,8 +25,9 @@
 
 #define err_set(e, err, fmt, ...) \
     ((e)->error_setg_win32((e)->errp, err, fmt, ## __VA_ARGS__))
+/* Bad idea, works only when (e)->errp != NULL: */
 #define err_is_set(e) ((e)->errp && *(e)->errp)
-
+/* To lift this restriction, error_propagate(), like we do in QEMU code */
 
 /* Handle to VSSAPI.DLL */
 static HMODULE hLib;
diff --git a/qga/vss-win32/requester.h b/qga/vss-win32/requester.h
index 0a8d048874..34be5c1d11 100644
--- a/qga/vss-win32/requester.h
+++ b/qga/vss-win32/requester.h
@@ -27,7 +27,7 @@ typedef void (*ErrorSetFunc)(struct Error **errp, int win32_err,
                              const char *fmt, ...) GCC_FMT_ATTR(3, 4);
 typedef struct ErrorSet {
     ErrorSetFunc error_setg_win32;
-    struct Error **errp;
+    struct Error **errp;        /* restriction: must not be null */
 } ErrorSet;
 
 STDAPI requester_init(void);