diff --git a/tests/utils_test.py b/tests/utils_test.py
index d4a3060..eb056bd 100644
--- a/tests/utils_test.py
+++ b/tests/utils_test.py
@@ -24,13 +24,15 @@ def test_load_single_seq_fasta():
         utils.load_single_seq_fasta(infile)
 
 
-def test_amplicons_json_to_bed():
+def test_amplicons_json_to_bed_and_range():
     json_in = os.path.join(data_dir, "amplicons_json_to_bed.json")
     expect_bed = os.path.join(data_dir, "amplicons_json_to_bed.bed")
     tmp_out = "tmp.amplicons_json_to_bed.bed"
     subprocess.check_output(f"rm -f {tmp_out}", shell=True)
-    utils.amplicons_json_to_bed(json_in, tmp_out)
+    got_start, got_end = utils.amplicons_json_to_bed_and_range(json_in, tmp_out)
     assert filecmp.cmp(tmp_out, expect_bed, shallow=False)
+    assert got_start == 100
+    assert got_end == 250
     os.unlink(tmp_out)
 
 
diff --git a/viridian_workflow/one_sample_pipeline.py b/viridian_workflow/one_sample_pipeline.py
index 4fde38e..3a8537e 100644
--- a/viridian_workflow/one_sample_pipeline.py
+++ b/viridian_workflow/one_sample_pipeline.py
@@ -2,7 +2,12 @@
 import os
 
 from viridian_workflow import minimap, qcovid, sample_reads, varifier
-from viridian_workflow.utils import amplicons_json_to_bed, check_file, run_process, rm
+from viridian_workflow.utils import (
+    amplicons_json_to_bed_and_range,
+    check_file,
+    run_process,
+    rm,
+)
 
 
 def check_tech(tech):
@@ -57,7 +62,9 @@ def run_one_sample(
 
     os.mkdir(outdir)
     amplicon_bed = os.path.join(outdir, "amplicons.bed")
-    amplicons_json_to_bed(amplicon_json, amplicon_bed)
+    amplicons_start, amplicons_end = amplicons_json_to_bed_and_range(
+        amplicon_json, amplicon_bed
+    )
     if paired:
         all_reads_bam = minimap.run(outdir, ref_genome, fq1, fq2)
     else:
@@ -91,7 +98,13 @@ def run_one_sample(
 
     masked_fasta = qcovid.self_qc(outdir, assembly, self_map)
 
-    vcf = varifier.run(varifier_out, ref_genome, masked_fasta)
+    vcf = varifier.run(
+        varifier_out,
+        ref_genome,
+        masked_fasta,
+        min_coord=amplicons_start,
+        max_coord=amplicons_end,
+    )
     check_file(vcf)
 
     # clean up intermediate files
diff --git a/viridian_workflow/utils.py b/viridian_workflow/utils.py
index afbd1f8..c7dbf2e 100644
--- a/viridian_workflow/utils.py
+++ b/viridian_workflow/utils.py
@@ -49,17 +49,27 @@ def run_process(cmd, ignore_error=False, stdout=None):
         logging.error(result.stderr)
 
 
-def amplicons_json_to_bed(infile, outfile):
+def amplicons_json_to_bed_and_range(infile, outfile):
+    """Converts the amplicons JSON file to a BED file, which is used in
+    various stages of the pipeline. Returns the 0-based inclusive coordinates
+    of the start of the first amplicon and end of the last amplicon, as
+    a tuple (start, end)"""
     with open(infile) as f:
         data = json.load(f)
 
+    start = float("inf")
+    end = -1
+
     data_out = []
     for amplicon, d in data["amplicons"].items():
         data_out.append((amplicon, d["start"], d["end"] + 1))
+        start = min(start, d["start"])
+        end = max(end, d["end"])
     data_out.sort(key=itemgetter(1))
     with open(outfile, "w") as f:
         for t in data_out:
             print(*t, sep="\t", file=f)
+    return start, end
 
 
 def load_amplicons_bed_file(infile):
diff --git a/viridian_workflow/varifier.py b/viridian_workflow/varifier.py
index a3a25dc..2017dd0 100644
--- a/viridian_workflow/varifier.py
+++ b/viridian_workflow/varifier.py
@@ -6,8 +6,14 @@
 from viridian_workflow.utils import run_process, check_file
 
 
-def run(outdir, ref_genome, assembly):
+def run(outdir, ref_genome, assembly, min_coord=None, max_coord=None):
     vcf = os.path.join(outdir, "04.truth.vcf")
-    run_process(f"varifier make_truth_vcf {assembly} {ref_genome} {outdir}")
+    options = ["--global_align"]
+    if min_coord is not None:
+        options.append(f"--global_align_min_coord {min_coord + 1}")
+    if max_coord is not None:
+        options.append(f"--global_align_max_coord {max_coord + 1}")
+    options = " ".join(options)
+    run_process(f"varifier make_truth_vcf {options} {assembly} {ref_genome} {outdir}")
     check_file(vcf)
     return vcf