diff --git a/CHANGELOG b/CHANGELOG
index 94d918a..abcedf9 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -10,6 +10,9 @@
 
  * Fixed handling of disks and volumes with 4k sectors (issue #45).
 
+ * Add an option to allow TRIM (discards) on the mapped volume
+   (issue #47).
+
 
 2013-07-31 Version 1.1 - Alex Hornung <alex@alexhornung.com>
 
diff --git a/main.c b/main.c
index 586a2a3..448ed73 100644
--- a/main.c
+++ b/main.c
@@ -155,6 +155,8 @@ usage(void)
 	    "\t Protect a hidden volume when mounting the outer volume.\n"
 	    " -s <disk path>, --system-encryption=<disk path>\n"
 	    "\t Specifies that the disk (e.g. /dev/da0) is using system encryption.\n"
+	    " -t, --allow-trim\n"
+	    "\t Allow discards (TRIM command) on mapped volume.\n"
 	    " --fde\n"
 	    "\t Specifies that the disk (e.g. /dev/da0) is using full disk encryption.\n"
 	    " --use-backup\n"
@@ -192,6 +194,7 @@ static struct option longopts[] = {
 	{ "protect-hidden",	no_argument,		NULL, 'e' },
 	{ "device",		required_argument,	NULL, 'd' },
 	{ "system-encryption",	required_argument,	NULL, 's' },
+	{ "allow-trim",		no_argument,		NULL, 't' },
 	{ "fde",		no_argument,		NULL, FLAG_LONG_FDE },
 	{ "use-backup",		no_argument,		NULL, FLAG_LONG_USE_BACKUP },
 	{ "modify",		no_argument,		NULL, FLAG_LONG_MOD },
@@ -242,7 +245,7 @@ main(int argc, char *argv[])
 	n_hkeyfiles = 0;
 	n_newkeyfiles = 0;
 
-	while ((ch = getopt_long(argc, argv, "a:b:cd:ef:ghij:k:m:s:u:vwx:y:z",
+	while ((ch = getopt_long(argc, argv, "a:b:cd:ef:ghij:k:m:s:tu:vwx:y:z",
 	    longopts, NULL)) != -1) {
 		switch(ch) {
 		case 'a':
@@ -300,6 +303,9 @@ main(int argc, char *argv[])
 			flags |= TC_FLAG_SYS;
 			sys_dev = optarg;
 			break;
+		case 't':
+			flags |= TC_FLAG_ALLOW_TRIM;
+			break;
 		case 'u':
 			unmap_vol = 1;
 			map_name = optarg;
diff --git a/tcplay.3 b/tcplay.3
index 62a8f46..8f33b5a 100644
--- a/tcplay.3
+++ b/tcplay.3
@@ -28,7 +28,7 @@
 .\" OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd July 30, 2013
+.Dd December 07, 2013
 .Dt TCPLAY 3
 .Os
 .Sh NAME
@@ -115,6 +115,7 @@ typedef struct tc_api_opts {
 	const char	*tc_system_device;
 	int		tc_use_fde;
 	int		tc_use_backup;
+	int		tc_allow_trim;
 
 	/* Fields for modify */
 	const char	*tc_new_passphrase;
@@ -412,6 +413,11 @@ is specified,
 .Nm tcplay
 will use the backup headers at the end of a volume
 instead of the primary headers to access it.
+If
+.Fa tc_allow_trim
+is specified,
+.Nm tcplay
+will allow TRIM (discards) on the mapped volume.
 .Pp
 The
 .Fn tc_api_unmap_volume
diff --git a/tcplay.8 b/tcplay.8
index ad0a4cc..b63c9d7 100644
--- a/tcplay.8
+++ b/tcplay.8
@@ -29,7 +29,7 @@
 .\" OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd July 29, 2013
+.Dd December 07, 2013
 .Dt TCPLAY 8
 .Os
 .Sh NAME
@@ -66,6 +66,7 @@
 .Op Fl f Ar keyfile_hidden
 .Op Fl k Ar keyfile
 .Op Fl s Ar system_device
+.Op Fl t
 .Op Fl -fde
 .Op Fl -use-backup
 .Nm
@@ -271,6 +272,14 @@ to access the volume.
 .El
 .Pp
 Additional options only for the
+.Fl -map
+command are:
+.Bl -tag -width indent
+.It Fl t , Fl -allow-trim
+This option enables TRIM (discard) support on the mapped volume.
+.El
+.Pp
+Additional options only for the
 .Fl -modify
 command are:
 .Bl -tag -width indent
diff --git a/tcplay.c b/tcplay.c
index 0d65467..2228f02 100644
--- a/tcplay.c
+++ b/tcplay.c
@@ -1489,7 +1489,7 @@ dm_get_table(const char *name)
 				++c;
 			}
 
-			if (c != 5) {
+			if (c < 5) {
 				tc_log(1, "could not get all the info required from "
 				    "the table\n");
 				goto error;
@@ -1796,12 +1796,13 @@ dm_setup(const char *mapname, struct tcplay_info *info)
 			start = INFO_TO_DM_BLOCKS(info, offset);
 		}
 
-		/* aes-cbc-essiv:sha256 7997f8af... 0 /dev/ad0s0a 8 */
-		/*			   iv off---^  block off--^ */
-		snprintf(params, 512, "%s %s %"PRIu64 " %s %"PRIu64,
+		/* aes-cbc-essiv:sha256 7997f8af... 0 /dev/ad0s0a 8 <opts> */
+		/*			   iv off---^  block off--^ <opts> */
+		snprintf(params, 512, "%s %s %"PRIu64 " %s %"PRIu64 " %s",
 		    cipher_chain->cipher->dm_crypt_str, cipher_chain->dm_key,
 		    (uint64_t)INFO_TO_DM_BLOCKS(info, skip), dev,
-		    (uint64_t)offset);
+		    (uint64_t)offset,
+		    TC_FLAG_SET(info->flags, ALLOW_TRIM) ? "1 allow_discards" : "");
 #ifdef DEBUG
 		printf("Params: %s\n", params);
 #endif
diff --git a/tcplay.h b/tcplay.h
index 11e7082..c66305d 100644
--- a/tcplay.h
+++ b/tcplay.h
@@ -67,6 +67,7 @@
 #define TC_FLAG_FDE		0x0002
 #define TC_FLAG_BACKUP		0x0004
 #define TC_FLAG_ONLY_RESTORE	0x0008
+#define TC_FLAG_ALLOW_TRIM	0x0010
 
 #define TC_FLAG_SET(f, x)	((f & TC_FLAG_##x) == TC_FLAG_##x)
 
diff --git a/tcplay_api.c b/tcplay_api.c
index 5247cf5..aa28b17 100644
--- a/tcplay_api.c
+++ b/tcplay_api.c
@@ -178,6 +178,8 @@ tc_api_map_volume(tc_api_opts *api_opts)
 		flags |= TC_FLAG_FDE;
 	if (api_opts->tc_use_backup)
 		flags |= TC_FLAG_BACKUP;
+	if (api_opts->tc_allow_trim)
+		flags |= TC_FLAG_ALLOW_TRIM;
 
 	err = map_volume(api_opts->tc_map_name, api_opts->tc_device,
 	    flags, api_opts->tc_system_device,
diff --git a/tcplay_api.h b/tcplay_api.h
index 10001b1..6082799 100644
--- a/tcplay_api.h
+++ b/tcplay_api.h
@@ -61,6 +61,7 @@ typedef struct tc_api_opts {
 	const char	*tc_system_device;
 	int		tc_use_fde;
 	int		tc_use_backup;
+	int		tc_allow_trim;
 
 	/* Fields for modify */
 	const char	*tc_new_passphrase;
diff --git a/test/features/support/env.rb b/test/features/support/env.rb
index 3ff0794..78c240e 100644
--- a/test/features/support/env.rb
+++ b/test/features/support/env.rb
@@ -28,6 +28,7 @@ class TCApiOpts < FFI::Struct
            :tc_system_device,         :pointer,
            :tc_use_fde,               :int,
            :tc_use_backup,            :int,
+           :tc_allow_trim,            :int,
 
     # Fields for modify
            :tc_new_passphrase,        :pointer,