diff --git a/jmemdos.c b/jmemdos.c
index 77fb5ad..60b45c6 100644
--- a/jmemdos.c
+++ b/jmemdos.c
@@ -1,7 +1,7 @@
 /*
  * jmemdos.c
  *
- * Copyright (C) 1992-1996, Thomas G. Lane.
+ * Copyright (C) 1992-1997, Thomas G. Lane.
  * This file is part of the Independent JPEG Group's software.
  * For conditions of distribution and use, see the accompanying README file.
  *
@@ -77,6 +77,10 @@
 #define READ_BINARY	"rb"
 #endif
 
+#ifndef USE_MSDOS_MEMMGR	/* make sure user got configuration right */
+  You forgot to define USE_MSDOS_MEMMGR in jconfig.h. /* deliberate syntax error */
+#endif
+
 #if MAX_ALLOC_CHUNK >= 65535L	/* make sure jconfig.h got this right */
   MAX_ALLOC_CHUNK should be less than 64K. /* deliberate syntax error */
 #endif