diff --git a/haptools/data/genotypes.py b/haptools/data/genotypes.py
index 7838c665..678d00b7 100644
--- a/haptools/data/genotypes.py
+++ b/haptools/data/genotypes.py
@@ -113,7 +113,7 @@ def read(self, region: str = None, samples: list[str] = None):
         # transpose the GT matrix so that samples are rows and variants are columns
         self.data = self.data.transpose((1, 0, 2))
 
-    def check_biallelic(self):
+    def check_biallelic(self, discard_also=False):
         """
         Check that each genotype is composed of only two alleles
 
@@ -126,6 +126,11 @@ def check_biallelic(self):
             converted to bool
         ValueError
             If any of the genotypes have more than two alleles
+
+        Parameters
+        ----------
+        discard_also : bool, optional
+            If True, discard any multiallelic variants without raising a ValueError
         """
         if self.data.dtype == np.bool_:
             raise AssertionError("All genotypes are already biallelic")
@@ -134,11 +139,15 @@ def check_biallelic(self):
         multiallelic = np.any(self.data[:, :, :2] > 1, axis=2)
         if np.any(multiallelic):
             samp_idx, variant_idx = np.nonzero(multiallelic)
-            raise ValueError(
-                "Variant with ID {} at POS {}:{} is multiallelic for sample {}".format(
-                    *tuple(self.variants[variant_idx[0]])[:3], self.samples[samp_idx[0]]
+            if discard_also:
+                self.data = np.delete(self.data, variant_idx, axis=1)
+                self.variants = np.delete(self.variants, variant_idx)
+            else:
+                raise ValueError(
+                    "Variant with ID {} at POS {}:{} is multiallelic for sample {}".format(
+                        *tuple(self.variants[variant_idx[0]])[:3], self.samples[samp_idx[0]]
+                    )
                 )
-            )
         self.data = self.data.astype(np.bool_)
 
     def check_phase(self):
diff --git a/pyproject.toml b/pyproject.toml
index 2340a3fc..b2416d57 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -55,7 +55,7 @@ haptools = 'haptools.__main__:main'
 
 [tool.black]
 line-length = 88
-experimental-string-processing = true
+preview = true
 
 [build-system]
 requires = ["poetry-core>=1.0.0"]
diff --git a/tests/test_data.py b/tests/test_data.py
index 284c3b70..1093441e 100644
--- a/tests/test_data.py
+++ b/tests/test_data.py
@@ -78,6 +78,27 @@ def test_load_genotypes():
         gts.to_MAC()
 
 
+def test_load_genotypes_discard_multiallelic():
+    expected = get_expected_genotypes()
+
+    # can we load the data from the VCF?
+    gts = Genotypes(DATADIR.joinpath("simple.vcf"))
+    gts.read()
+
+    # make a copy for later
+    data_copy = gts.data.copy().astype(np.bool_)
+    variant_shape = list(gts.variants.shape)
+    variant_shape[0] -= 1
+
+    # force one of the SNPs to have more than one allele and check that it gets dicarded
+    gts.data[1, 1, 1] = 2
+    gts.check_biallelic(discard_also=True)
+
+    data_copy_without_biallelic = np.delete(data_copy, [1], axis=1)
+    np.testing.assert_equal(gts.data, data_copy_without_biallelic)
+    assert gts.variants.shape == tuple(variant_shape)
+
+
 def test_load_genotypes_subset():
     expected = get_expected_genotypes()