diff --git a/winpr/include/winpr/wlog.h b/winpr/include/winpr/wlog.h
index fc8a67703..f8e1480c9 100644
--- a/winpr/include/winpr/wlog.h
+++ b/winpr/include/winpr/wlog.h
@@ -111,6 +111,7 @@ WINPR_API BOOL WLog_PrintMessageVA(wLog* log, wLogMessage* message, va_list args
 	do { \
 		if (_log && _log_level >= WLog_GetLogLevel(_log)) { \
 			wLogMessage _log_message; \
+			memset(&_log_message, 0, sizeof(_log_message)); \
 			_log_message.Type = WLOG_MESSAGE_TEXT; \
 			_log_message.Level = _log_level; \
 			_log_message.FormatString = _fmt; \
@@ -125,6 +126,7 @@ WINPR_API BOOL WLog_PrintMessageVA(wLog* log, wLogMessage* message, va_list args
 	do { \
 		if (_log && _log_level >= WLog_GetLogLevel(_log)) { \
 			wLogMessage _log_message; \
+			memset(&_log_message, 0, sizeof(_log_message)); \
 			_log_message.Type = WLOG_MESSAGE_TEXT; \
 			_log_message.Level = _log_level; \
 			_log_message.FormatString = _fmt; \
@@ -139,6 +141,7 @@ WINPR_API BOOL WLog_PrintMessageVA(wLog* log, wLogMessage* message, va_list args
 	do { \
 		if (_log && _log_level >= WLog_GetLogLevel(_log)) { \
 			wLogMessage _log_message; \
+			memset(&_log_message, 0, sizeof(_log_message)); \
 			_log_message.Type = WLOG_MESSAGE_DATA; \
 			_log_message.Level = _log_level; \
 			_log_message.FormatString = NULL; \
@@ -153,6 +156,7 @@ WINPR_API BOOL WLog_PrintMessageVA(wLog* log, wLogMessage* message, va_list args
 	do { \
 		if (_log && _log_level >= WLog_GetLogLevel(_log)) { \
 			wLogMessage _log_message; \
+			memset(&_log_message, 0, sizeof(_log_message)); \
 			_log_message.Type = WLOG_MESSAGE_IMAGE; \
 			_log_message.Level = _log_level; \
 			_log_message.FormatString = NULL; \
@@ -167,6 +171,7 @@ WINPR_API BOOL WLog_PrintMessageVA(wLog* log, wLogMessage* message, va_list args
 	do { \
 		if (_log && _log_level >= WLog_GetLogLevel(_log)) { \
 			wLogMessage _log_message; \
+			memset(&_log_message, 0, sizeof(_log_message)); \
 			_log_message.Type = WLOG_MESSAGE_PACKET; \
 			_log_message.Level = _log_level; \
 			_log_message.FormatString = NULL; \
diff --git a/winpr/libwinpr/utils/wlog/CallbackAppender.c b/winpr/libwinpr/utils/wlog/CallbackAppender.c
index 8a1719ff4..aec3865b9 100644
--- a/winpr/libwinpr/utils/wlog/CallbackAppender.c
+++ b/winpr/libwinpr/utils/wlog/CallbackAppender.c
@@ -49,6 +49,7 @@ static BOOL WLog_CallbackAppender_WriteMessage(wLog* log, wLogAppender* appender
 
 	if (!appender)
 		return FALSE;
+
 	message->PrefixString = prefix;
 	WLog_Layout_GetMessagePrefix(log, appender->Layout, message);
 
@@ -62,11 +63,15 @@ static BOOL WLog_CallbackAppender_WriteMessage(wLog* log, wLogAppender* appender
 
 static BOOL WLog_CallbackAppender_WriteDataMessage(wLog* log, wLogAppender* appender, wLogMessage* message)
 {
-
+	char prefix[WLOG_MAX_PREFIX_SIZE];
 	wLogCallbackAppender* callbackAppender;
+
 	if (!appender)
 		return FALSE;
 
+	message->PrefixString = prefix;
+	WLog_Layout_GetMessagePrefix(log, appender->Layout, message);
+
 	callbackAppender = (wLogCallbackAppender *)appender;
 	if (callbackAppender->callbacks && callbackAppender->callbacks->data)
 		return callbackAppender->callbacks->data(message);
@@ -76,10 +81,15 @@ static BOOL WLog_CallbackAppender_WriteDataMessage(wLog* log, wLogAppender* appe
 
 static BOOL WLog_CallbackAppender_WriteImageMessage(wLog* log, wLogAppender* appender, wLogMessage* message)
 {
+	char prefix[WLOG_MAX_PREFIX_SIZE];
 	wLogCallbackAppender* callbackAppender;
+
 	if (!appender)
 		return FALSE;
 
+	message->PrefixString = prefix;
+	WLog_Layout_GetMessagePrefix(log, appender->Layout, message);
+
 	callbackAppender = (wLogCallbackAppender *)appender;
 	if (callbackAppender->callbacks && callbackAppender->callbacks->image)
 		return callbackAppender->callbacks->image(message);
@@ -89,10 +99,15 @@ static BOOL WLog_CallbackAppender_WriteImageMessage(wLog* log, wLogAppender* app
 
 static BOOL WLog_CallbackAppender_WritePacketMessage(wLog* log, wLogAppender* appender, wLogMessage* message)
 {
+	char prefix[WLOG_MAX_PREFIX_SIZE];
 	wLogCallbackAppender* callbackAppender;
+
 	if (!appender)
 		return FALSE;
 
+	message->PrefixString = prefix;
+	WLog_Layout_GetMessagePrefix(log, appender->Layout, message);
+
 	callbackAppender = (wLogCallbackAppender *)appender;
 	if (callbackAppender->callbacks && callbackAppender->callbacks->package)
 		return callbackAppender->callbacks->package(message);