diff --git a/common/iobuf.c b/common/iobuf.c
index 284408b1f..5e6624f20 100644
--- a/common/iobuf.c
+++ b/common/iobuf.c
@@ -138,13 +138,6 @@ typedef struct
 #define OP_MIN_PARTIAL_CHUNK	  512
 #define OP_MIN_PARTIAL_CHUNK_2POW 9
 
-enum
-  {
-    BLOCK_FILTER_INPUT=1,
-    BLOCK_FILTER_OUTPUT=2,
-    BLOCK_FILTER_TEMP=3
-  };
-
 /* The context we use for the block filter (used to handle OpenPGP
    length information header).  */
 typedef struct
@@ -1001,7 +994,7 @@ block_filter (void *opaque, int control, iobuf_t chain, byte * buffer,
 	log_debug ("init block_filter %p\n", a);
       if (a->partial)
 	a->count = 0;
-      else if (a->use == BLOCK_FILTER_INPUT)
+      else if (a->use == IOBUF_INPUT)
 	a->count = a->size = 0;
       else
 	a->count = a->size;	/* force first length bytes */
@@ -1015,7 +1008,7 @@ block_filter (void *opaque, int control, iobuf_t chain, byte * buffer,
     }
   else if (control == IOBUFCTRL_FREE)
     {
-      if (a->use == BLOCK_FILTER_OUTPUT)
+      if (a->use == IOBUF_OUTPUT)
 	{			/* write the end markers */
 	  if (a->partial)
 	    {
@@ -1105,9 +1098,8 @@ iobuf_print_chain (iobuf_t a)
 
 /* Allocate a new io buffer, with no function assigned.
 
-   USE is the desired usage: BLOCK_FILTER_INPUT for input,
-   BLOCK_FILTER_OUTPUT for output, or BLOCK_FILTER_TEMP for a temp
-   buffer.
+   USE is the desired usage: IOBUF_INPUT for input, IOBUF_OUTPUT for
+   output, or IOBUF_TEMP for a temp buffer.
 
    BUFSIZE is a suggested buffer size.
  */
@@ -1117,9 +1109,7 @@ iobuf_alloc (int use, size_t bufsize)
   iobuf_t a;
   static int number = 0;
 
-  assert (use == BLOCK_FILTER_INPUT
-	  || use == BLOCK_FILTER_OUTPUT
-	  || use == BLOCK_FILTER_TEMP);
+  assert (use == IOBUF_INPUT || use == IOBUF_OUTPUT || use == IOBUF_TEMP);
 
   a = xcalloc (1, sizeof *a);
   a->use = use;
@@ -1151,7 +1141,7 @@ iobuf_close (iobuf_t a)
   for (; a && !rc; a = a2)
     {
       a2 = a->chain;
-      if (a->use == BLOCK_FILTER_OUTPUT && (rc = iobuf_flush (a)))
+      if (a->use == IOBUF_OUTPUT && (rc = iobuf_flush (a)))
 	log_error ("iobuf_flush failed on close: %s\n", gpg_strerror (rc));
 
       if (DBG_IOBUF)
@@ -1181,7 +1171,7 @@ iobuf_cancel (iobuf_t a)
   char *remove_name = NULL;
 #endif
 
-  if (a && a->use == BLOCK_FILTER_OUTPUT)
+  if (a && a->use == IOBUF_OUTPUT)
     {
       s = iobuf_get_real_fname (a);
       if (s && *s)
@@ -1233,7 +1223,7 @@ iobuf_temp ()
 {
   iobuf_t a;
 
-  a = iobuf_alloc (3, IOBUF_BUFFER_SIZE);
+  a = iobuf_alloc (IOBUF_TEMP, IOBUF_BUFFER_SIZE);
 
   return a;
 }
@@ -1244,7 +1234,7 @@ iobuf_temp_with_content (const char *buffer, size_t length)
   iobuf_t a;
   int i;
 
-  a = iobuf_alloc (3, length);
+  a = iobuf_alloc (IOBUF_TEMP, length);
   /* memcpy (a->d.buf, buffer, length); */
   for (i=0; i < length; i++)
     a->d.buf[i] = buffer[i];
@@ -1332,7 +1322,7 @@ iobuf_open (const char *fname)
     return iobuf_fdopen (translate_file_handle (fd, 0), "rb");
   else if ((fp = fd_cache_open (fname, "rb")) == GNUPG_INVALID_FD)
     return NULL;
-  a = iobuf_alloc (1, IOBUF_BUFFER_SIZE);
+  a = iobuf_alloc (IOBUF_INPUT, IOBUF_BUFFER_SIZE);
   fcx = xmalloc (sizeof *fcx + strlen (fname));
   fcx->fp = fp;
   fcx->print_only_name = print_only;
@@ -1361,7 +1351,8 @@ do_iobuf_fdopen (int fd, const char *mode, int keep_open)
 
   fp = INT2FD (fd);
 
-  a = iobuf_alloc (strchr (mode, 'w') ? 2 : 1, IOBUF_BUFFER_SIZE);
+  a = iobuf_alloc (strchr (mode, 'w') ? IOBUF_OUTPUT : IOBUF_INPUT,
+		   IOBUF_BUFFER_SIZE);
   fcx = xmalloc (sizeof *fcx + 20);
   fcx->fp = fp;
   fcx->print_only_name = 1;
@@ -1401,7 +1392,8 @@ iobuf_esopen (estream_t estream, const char *mode, int keep_open)
   file_es_filter_ctx_t *fcx;
   size_t len;
 
-  a = iobuf_alloc (strchr (mode, 'w') ? 2 : 1, IOBUF_BUFFER_SIZE);
+  a = iobuf_alloc (strchr (mode, 'w') ? IOBUF_OUTPUT : IOBUF_INPUT,
+		   IOBUF_BUFFER_SIZE);
   fcx = xtrymalloc (sizeof *fcx + 30);
   fcx->fp = estream;
   fcx->print_only_name = 1;
@@ -1426,7 +1418,8 @@ iobuf_sockopen (int fd, const char *mode)
   sock_filter_ctx_t *scx;
   size_t len;
 
-  a = iobuf_alloc (strchr (mode, 'w') ? 2 : 1, IOBUF_BUFFER_SIZE);
+  a = iobuf_alloc (strchr (mode, 'w') ? IOBUF_OUTPUT : IOBUF_INPUT,
+		   IOBUF_BUFFER_SIZE);
   scx = xmalloc (sizeof *scx + 25);
   scx->sock = fd;
   scx->print_only_name = 1;
@@ -1468,7 +1461,7 @@ iobuf_create (const char *fname, int mode700)
     return iobuf_fdopen (translate_file_handle (fd, 1), "wb");
   else if ((fp = direct_open (fname, "wb", mode700)) == GNUPG_INVALID_FD)
     return NULL;
-  a = iobuf_alloc (2, IOBUF_BUFFER_SIZE);
+  a = iobuf_alloc (IOBUF_OUTPUT, IOBUF_BUFFER_SIZE);
   fcx = xmalloc (sizeof *fcx + strlen (fname));
   fcx->fp = fp;
   fcx->print_only_name = print_only;
@@ -1499,7 +1492,7 @@ iobuf_openrw (const char *fname)
     return NULL;
   else if ((fp = direct_open (fname, "r+b", 0)) == GNUPG_INVALID_FD)
     return NULL;
-  a = iobuf_alloc (2, IOBUF_BUFFER_SIZE);
+  a = iobuf_alloc (IOBUF_OUTPUT, IOBUF_BUFFER_SIZE);
   fcx = xmalloc (sizeof *fcx + strlen (fname));
   fcx->fp = fp;
   strcpy (fcx->fname, fname);
@@ -1624,7 +1617,7 @@ iobuf_push_filter2 (iobuf_t a,
   if (a->directfp)
     BUG ();
 
-  if (a->use == BLOCK_FILTER_OUTPUT && (rc = iobuf_flush (a)))
+  if (a->use == IOBUF_OUTPUT && (rc = iobuf_flush (a)))
     return rc;
 
   if (a->subno >= MAX_NESTING_FILTER)
@@ -1649,11 +1642,11 @@ iobuf_push_filter2 (iobuf_t a,
   a->filter_ov = NULL;
   a->filter_ov_owner = 0;
   a->filter_eof = 0;
-  if (a->use == BLOCK_FILTER_TEMP)
+  if (a->use == IOBUF_TEMP)
     /* make a write stream from a temp stream */
-    a->use = BLOCK_FILTER_OUTPUT;
+    a->use = IOBUF_OUTPUT;
 
-  if (a->use == BLOCK_FILTER_OUTPUT)
+  if (a->use == IOBUF_OUTPUT)
     {				/* allocate a fresh buffer for the
                                    original stream */
       b->d.buf = xmalloc (a->d.size);
@@ -1732,7 +1725,7 @@ pop_filter (iobuf_t a, int (*f) (void *opaque, int control,
     log_bug ("pop_filter(): filter function not found\n");
 
   /* flush this stream if it is an output stream */
-  if (a->use == BLOCK_FILTER_OUTPUT && (rc = iobuf_flush (b)))
+  if (a->use == IOBUF_OUTPUT && (rc = iobuf_flush (b)))
     {
       log_error ("iobuf_flush failed in pop_filter: %s\n", gpg_strerror (rc));
       return rc;
@@ -1791,7 +1784,7 @@ underflow (iobuf_t a)
   int rc;
 
   assert (a->d.start == a->d.len);
-  if (a->use == BLOCK_FILTER_TEMP)
+  if (a->use == IOBUF_TEMP)
     return -1;			/* EOF because a temp buffer can't do an underflow */
 
   if (a->filter_eof)
@@ -1853,7 +1846,7 @@ underflow (iobuf_t a)
 /*  	    if( a->no == 1 ) */
 /*                   log_hexdump ("     data:", a->d.buf, len); */
 	}
-      if (a->use == BLOCK_FILTER_INPUT && rc == -1)
+      if (a->use == IOBUF_INPUT && rc == -1)
 	{			/* EOF: we can remove the filter */
 	  size_t dummy_len = 0;
 
@@ -1915,7 +1908,7 @@ iobuf_flush (iobuf_t a)
   if (a->directfp)
     return 0;
 
-  if (a->use == BLOCK_FILTER_TEMP)
+  if (a->use == IOBUF_TEMP)
     {				/* increase the temp buffer */
       unsigned char *newbuf;
       size_t newsize = a->d.size + IOBUF_BUFFER_SIZE;
@@ -1930,7 +1923,7 @@ iobuf_flush (iobuf_t a)
       a->d.size = newsize;
       return 0;
     }
-  else if (a->use != BLOCK_FILTER_OUTPUT)
+  else if (a->use != IOBUF_OUTPUT)
     log_bug ("flush on non-output iobuf\n");
   else if (!a->filter)
     log_bug ("iobuf_flush: no filter\n");
@@ -2346,7 +2339,7 @@ iobuf_seek (iobuf_t a, off_t newpos)
 	}
       clearerr (fp);
     }
-  else if (a->use != BLOCK_FILTER_TEMP)
+  else if (a->use != IOBUF_TEMP)
     {
       for (; a; a = a->chain)
 	{
@@ -2374,7 +2367,7 @@ iobuf_seek (iobuf_t a, off_t newpos)
 #endif
     }
   /* Discard the buffer unless it is a temp stream.  */
-  if (a->use != BLOCK_FILTER_TEMP)
+  if (a->use != IOBUF_TEMP)
     a->d.len = 0;
   a->d.start = 0;
   a->nbytes = 0;
@@ -2454,11 +2447,11 @@ iobuf_set_partial_block_mode (iobuf_t a, size_t len)
 {
   block_filter_ctx_t *ctx = xcalloc (1, sizeof *ctx);
 
-  assert (a->use == BLOCK_FILTER_INPUT || a->use == BLOCK_FILTER_OUTPUT);
+  assert (a->use == IOBUF_INPUT || a->use == IOBUF_OUTPUT);
   ctx->use = a->use;
   if (!len)
     {
-      if (a->use == BLOCK_FILTER_INPUT)
+      if (a->use == IOBUF_INPUT)
 	log_debug ("pop_filter called in set_partial_block_mode"
 		   " - please report\n");
       pop_filter (a, block_filter, NULL);
diff --git a/common/iobuf.h b/common/iobuf.h
index 3889459e3..23b1d091e 100644
--- a/common/iobuf.h
+++ b/common/iobuf.h
@@ -55,6 +55,13 @@ typedef enum
     IOBUF_IOCTL_FSYNC            = 4  /* Uses ptrval.  */
   } iobuf_ioctl_t;
 
+enum
+  {
+    IOBUF_INPUT=1,
+    IOBUF_OUTPUT=2,
+    IOBUF_TEMP=3
+  };
+
 
 typedef struct iobuf_struct *iobuf_t;
 typedef struct iobuf_struct *IOBUF;  /* Compatibility with gpg 1.4. */
@@ -62,7 +69,9 @@ typedef struct iobuf_struct *IOBUF;  /* Compatibility with gpg 1.4. */
 /* fixme: we should hide most of this stuff */
 struct iobuf_struct
 {
-  int use;			/* 1 input , 2 output, 3 temp */
+  /* The type of filter.  Either IOBUF_INPUT, IOBUF_OUTPUT or
+     IOBUF_TEMP.  */
+  int use;
   off_t nlimit;
   off_t nbytes;			/* Used together with nlimit. */
   off_t ntotal;			/* Total bytes read (position of stream). */
@@ -184,6 +193,8 @@ void iobuf_skip_rest (iobuf_t a, unsigned long n, int partial);
 
 #define iobuf_get_temp_buffer(a) ( (a)->d.buf )
 #define iobuf_get_temp_length(a) ( (a)->d.len )
-#define iobuf_is_temp(a)	 ( (a)->use == 3 )
+
+/* Whether the filter uses an in-memory buffer.  */
+#define iobuf_is_temp(a)	 ( (a)->use == IOBUF_TEMP )
 
 #endif /*GNUPG_COMMON_IOBUF_H*/