diff --git a/fastmap.c b/fastmap.c
index 18f3b0e..25bf822 100644
--- a/fastmap.c
+++ b/fastmap.c
@@ -55,7 +55,7 @@ int main_mem(int argc, char *argv[])
 
 	opt = mem_opt_init();
 	memset(&opt0, 0, sizeof(mem_opt_t));
-	while ((c = getopt(argc, argv, "epaFMCSPHVYjk:c:v:s:r:t:R:A:B:O:E:U:w:L:d:T:Q:D:m:I:N:W:x:G:h:y:K:")) >= 0) {
+	while ((c = getopt(argc, argv, "epaFMCSPHVYjk:c:v:s:r:t:R:A:B:O:E:U:w:L:d:T:Q:D:m:I:N:W:x:G:h:y:K:X:")) >= 0) {
 		if (c == 'k') opt->min_seed_len = atoi(optarg), opt0.min_seed_len = 1;
 		else if (c == 'x') mode = optarg;
 		else if (c == 'w') opt->w = atoi(optarg), opt0.w = 1;
@@ -87,6 +87,7 @@ int main_mem(int argc, char *argv[])
 		else if (c == 'y') opt->max_mem_intv = atol(optarg), opt0.max_mem_intv = 1;
 		else if (c == 'C') copy_comment = 1;
 		else if (c == 'K') fixed_chunk_size = atoi(optarg);
+		else if (c == 'X') opt->mask_level = atof(optarg);
 		else if (c == 'h') {
 			opt0.max_XA_hits = opt0.max_XA_hits_alt = 1;
 			opt->max_XA_hits = opt->max_XA_hits_alt = strtol(optarg, &p, 10);
diff --git a/main.c b/main.c
index f8f6995..a69ffeb 100644
--- a/main.c
+++ b/main.c
@@ -4,7 +4,7 @@
 #include "utils.h"
 
 #ifndef PACKAGE_VERSION
-#define PACKAGE_VERSION "0.7.10-r960-dirty"
+#define PACKAGE_VERSION "0.7.10-r963-dirty"
 #endif
 
 int bwa_fa2pac(int argc, char *argv[]);