diff --git a/reactos/dll/win32/kernel32/client/compname.c b/reactos/dll/win32/kernel32/client/compname.c
index 407850a85f3..06c11b63470 100644
--- a/reactos/dll/win32/kernel32/client/compname.c
+++ b/reactos/dll/win32/kernel32/client/compname.c
@@ -263,8 +263,15 @@ GetComputerNameExA(COMPUTER_NAME_FORMAT NameType,
     UNICODE_STRING UnicodeString;
     ANSI_STRING AnsiString;
     BOOL Result;
-    PWCHAR TempBuffer = RtlAllocateHeap( RtlGetProcessHeap(), 0, *nSize * sizeof(WCHAR) );
+    PWCHAR TempBuffer;
 
+    if (!lpBuffer)
+    {
+        SetLastError(ERROR_INVALID_PARAMETER);
+        return FALSE;
+    }
+
+    TempBuffer = RtlAllocateHeap(RtlGetProcessHeap(), 0, *nSize * sizeof(WCHAR));
     if (!TempBuffer)
     {
         SetLastError(ERROR_NOT_ENOUGH_MEMORY);