diff --git a/dlls/ntdll/signal_x86_64.c b/dlls/ntdll/signal_x86_64.c
index 0d2536017bd..e751082d722 100644
--- a/dlls/ntdll/signal_x86_64.c
+++ b/dlls/ntdll/signal_x86_64.c
@@ -2160,9 +2160,13 @@ NTSTATUS WINAPI NtSetContextThread( HANDLE handle, const CONTEXT *context )
 NTSTATUS WINAPI NtGetContextThread( HANDLE handle, CONTEXT *context )
 {
     NTSTATUS ret;
-    DWORD needed_flags = context->ContextFlags;
+    DWORD needed_flags;
     BOOL self = (handle == GetCurrentThread());
 
+    if (!context) return STATUS_INVALID_PARAMETER;
+
+    needed_flags = context->ContextFlags;
+
     /* debug registers require a server call */
     if (context->ContextFlags & (CONTEXT_DEBUG_REGISTERS & ~CONTEXT_AMD64)) self = FALSE;