diff --git a/main.c b/main.c
index 9b91e69..0a3eaad 100644
--- a/main.c
+++ b/main.c
@@ -6,7 +6,7 @@
 #include "mmpriv.h"
 #include "getopt.h"
 
-#define MM_VERSION "2.9-r720"
+#define MM_VERSION "2.9-r741-dirty"
 
 #ifdef __linux__
 #include <sys/resource.h>
@@ -51,6 +51,7 @@ static struct option long_options[] = {
 	{ "all-chain",      no_argument,       0, 'P' },
 	{ "dual",           required_argument, 0, 0 },   // 26
 	{ "max-clip-ratio", required_argument, 0, 0 },   // 27
+	{ "min-occ-floor",  required_argument, 0, 0 },   // 28
 	{ "help",           no_argument,       0, 'h' },
 	{ "max-intron-len", required_argument, 0, 'G' },
 	{ "version",        no_argument,       0, 'V' },
@@ -164,6 +165,7 @@ int main(int argc, char *argv[])
 		else if (c == 0 && long_idx ==22) opt.flag |= MM_F_FOR_ONLY; // --for-only
 		else if (c == 0 && long_idx ==23) opt.flag |= MM_F_REV_ONLY; // --rev-only
 		else if (c == 0 && long_idx ==27) opt.max_clip_ratio = atof(optarg); // --max-clip-ratio
+		else if (c == 0 && long_idx ==28) opt.min_mid_occ = atoi(optarg); // --min-occ-floor
 		else if (c == 0 && long_idx == 14) { // --frag
 			yes_or_no(&opt, MM_F_FRAG_MODE, long_idx, optarg, 1);
 		} else if (c == 0 && long_idx == 15) { // --secondary
diff --git a/minimap.h b/minimap.h
index 4e3a617..ae68bfe 100644
--- a/minimap.h
+++ b/minimap.h
@@ -126,6 +126,7 @@ typedef struct {
 	int pe_ori, pe_bonus;
 
 	float mid_occ_frac;  // only used by mm_mapopt_update(); see below
+	int32_t min_mid_occ;
 	int32_t mid_occ;     // ignore seeds with occurrences above this threshold
 	int32_t max_occ;
 	int mini_batch_size; // size of a batch of query bases to process in parallel
diff --git a/minimap2.1 b/minimap2.1
index 6745ffa..f0c040a 100644
--- a/minimap2.1
+++ b/minimap2.1
@@ -217,6 +217,14 @@ on chains. Set
 .I INT
 to a large number to switch off this heurstics.
 .TP
+.BI --min-occ-floor \ INT
+Force minimap2 to always use k-mers occurring
+.I INT
+times or less [0]. In effect, the max occurrence threshold is set to
+the
+.RI max{ INT ,
+.BR -f }.
+.TP
 .B --no-long-join
 Disable the long gap patching heuristic. When this option is applied, the
 maximum alignment gap is mostly controlled by
@@ -433,18 +441,25 @@ is determined by the sequencing error mode.
 .B asm5
 Long assembly to reference mapping
 .RB ( -k19
-.B -w19 -A1 -B19 -O39,81 -E3,1 -s200
-.BR -z200 ).
+.B -w19 -A1 -B19 -O39,81 -E3,1 -s200 -z200
+.BR --min-occ-floor=100 ).
 Typically, the alignment will not extend to regions with 5% or higher sequence
 divergence. Only use this preset if the average divergence is far below 5%.
 .TP
 .B asm10
 Long assembly to reference mapping
 .RB ( -k19
-.B -w19 -A1 -B9 -O16,41 -E2,1 -s200
-.BR -z200 ).
+.B -w19 -A1 -B9 -O16,41 -E2,1 -s200 -z200
+.BR --min-occ-floor=100 ).
 Up to 10% sequence divergence.
 .TP
+.B asm20
+Long assembly to reference mapping
+.RB ( -k19
+.B -w10 -A1 -B6 -O6,26 -E2,1 -s200 -z200
+.BR --min-occ-floor=100 ).
+Up to 20% sequence divergence.
+.TP
 .B ava-pb
 PacBio all-vs-all overlap mapping
 .RB ( -Hk19
diff --git a/options.c b/options.c
index b98e0eb..e820484 100644
--- a/options.c
+++ b/options.c
@@ -51,6 +51,8 @@ void mm_mapopt_update(mm_mapopt_t *opt, const mm_idx_t *mi)
 		opt->flag |= MM_F_SPLICE;
 	if (opt->mid_occ <= 0)
 		opt->mid_occ = mm_idx_cal_max_occ(mi, opt->mid_occ_frac);
+	if (opt->mid_occ < opt->min_mid_occ)
+		opt->mid_occ = opt->min_mid_occ;
 	if (mm_verbose >= 3)
 		fprintf(stderr, "[M::%s::%.3f*%.2f] mid_occ = %d\n", __func__, realtime() - mm_realtime0, cputime() / (realtime() - mm_realtime0), opt->mid_occ);
 }
@@ -81,11 +83,19 @@ int mm_set_opt(const char *preset, mm_idxopt_t *io, mm_mapopt_t *mo)
 	} else if (strcmp(preset, "asm5") == 0) {
 		io->flag = 0, io->k = 19, io->w = 19;
 		mo->a = 1, mo->b = 19, mo->q = 39, mo->q2 = 81, mo->e = 3, mo->e2 = 1, mo->zdrop = mo->zdrop_inv = 200;
+		mo->min_mid_occ = 100;
 		mo->min_dp_max = 200;
 		mo->best_n = 50;
 	} else if (strcmp(preset, "asm10") == 0) {
 		io->flag = 0, io->k = 19, io->w = 19;
 		mo->a = 1, mo->b = 9, mo->q = 16, mo->q2 = 41, mo->e = 2, mo->e2 = 1, mo->zdrop = mo->zdrop_inv = 200;
+		mo->min_mid_occ = 100;
+		mo->min_dp_max = 200;
+		mo->best_n = 50;
+	} else if (strcmp(preset, "asm20") == 0) {
+		io->flag = 0, io->k = 19, io->w = 10;
+		mo->a = 1, mo->b = 4, mo->q = 6, mo->q2 = 26, mo->e = 2, mo->e2 = 1, mo->zdrop = mo->zdrop_inv = 200;
+		mo->min_mid_occ = 100;
 		mo->min_dp_max = 200;
 		mo->best_n = 50;
 	} else if (strcmp(preset, "short") == 0 || strcmp(preset, "sr") == 0) {
diff --git a/python/cmappy.pxd b/python/cmappy.pxd
index 532f6f5..3735307 100644
--- a/python/cmappy.pxd
+++ b/python/cmappy.pxd
@@ -34,6 +34,7 @@ cdef extern from "minimap.h":
 		float max_clip_ratio
 		int pe_ori, pe_bonus
 		float mid_occ_frac
+		int32_t min_mid_occ
 		int32_t mid_occ
 		int32_t max_occ
 		int mini_batch_size