diff --git a/dlls/advapi32/security.c b/dlls/advapi32/security.c
index 41a3aef638b..48d795f1042 100644
--- a/dlls/advapi32/security.c
+++ b/dlls/advapi32/security.c
@@ -3266,7 +3266,7 @@ static BOOL ParseStringSecurityDescriptorToSecurityDescriptor(
     LPBYTE lpNext = NULL;
     DWORD len;
 
-    *cBytes = 0;
+    *cBytes = sizeof(SECURITY_DESCRIPTOR);
 
     if (SecurityDescriptor)
         lpNext = ((LPBYTE) SecurityDescriptor) + sizeof(SECURITY_DESCRIPTOR);