diff --git a/include/comedi.h b/include/comedi.h
index 3e38f35..acfc22a 100644
--- a/include/comedi.h
+++ b/include/comedi.h
@@ -133,7 +133,6 @@ typedef unsigned short sampl_t;
 #define SDF_RUNNING	0x08000000	/* subdevice is acquiring data */
 #define SDF_LSAMPL	0x10000000	/* subdevice uses 32-bit samples */
 #define SDF_PACKED	0x20000000	/* subdevice can do packed DIO */
-#define SDF_MMAPPED	0x40000000	/* is currently mmap'ed */
 
 /* subdevice types */