diff --git a/deepvariant/pileup_image.py b/deepvariant/pileup_image.py
index cee82a07..d36ad2ec 100644
--- a/deepvariant/pileup_image.py
+++ b/deepvariant/pileup_image.py
@@ -35,6 +35,7 @@
 import itertools
 
 
+from absl import logging
 import numpy as np
 
 from third_party.nucleus.protos import reads_pb2
@@ -470,6 +471,12 @@ def _pileup_for_pair_of_alts(alt_alleles):
         else:
           alt_images = []
           for alt in alt_alleles:
+            if len(haplotype_sequences[alt]) != self.width:
+              logging.warning(
+                  'haplotype_sequences[alt] is %d long but pileup '
+                  'image width is %d. Giving up on this image',
+                  len(haplotype_sequences[alt]), self.width)
+              return None
             alt_image = self.build_pileup(
                 dv_call=dv_call,
                 refbases=haplotype_sequences[alt],
@@ -485,5 +492,13 @@ def _pileup_for_pair_of_alts(alt_alleles):
       else:
         return ref_image
 
-    return [(alts, _pileup_for_pair_of_alts(alts))
-            for alts in self._alt_allele_combinations(variant)]
+    retval = []
+    for alts in self._alt_allele_combinations(variant):
+      pileup = _pileup_for_pair_of_alts(alts)
+      # If the pileup is None, this can mean that we're near the edge of the
+      # contig, so one pileup width is invalid.
+      # Return None to indicate we couldn't process this variant.
+      if pileup is None:
+        return None
+      retval.append((alts, pileup))
+    return retval
diff --git a/deepvariant/pileup_image_test.py b/deepvariant/pileup_image_test.py
index 9b534fc5..cae2ccfa 100644
--- a/deepvariant/pileup_image_test.py
+++ b/deepvariant/pileup_image_test.py
@@ -1213,7 +1213,9 @@ def _expected_call(alts):
 
   def test_create_pileup_images_with_alt_align(self):
     self.dv_call.variant.alternate_bases[:] = ['C', 'T']
-    haplotype_sequences = {'C': 'seq for C', 'T': 'seq for T'}
+    seq_for_c = 'C' * self.pic.width
+    seq_for_t = 'T' * self.pic.width
+    haplotype_sequences = {'C': seq_for_c, 'T': seq_for_t}
     haplotype_alignments = {'C': 'reads for C', 'T': 'reads for T'}
 
     with mock.patch.object(
@@ -1256,17 +1258,33 @@ def _expected_alt_based_call(alts, refbases, reads):
           [
               # Pileup for 'C':
               _expected_ref_based_call(['C']),
-              _expected_alt_based_call(['C'], 'seq for C', 'reads for C'),
+              _expected_alt_based_call(['C'], seq_for_c, 'reads for C'),
               # Pileup for 'T':
               _expected_ref_based_call(['T']),
-              _expected_alt_based_call(['T'], 'seq for T', 'reads for T'),
+              _expected_alt_based_call(['T'], seq_for_t, 'reads for T'),
               # Pileup for 'C/T':
               _expected_ref_based_call(['C', 'T']),
-              _expected_alt_based_call(['C', 'T'], 'seq for C', 'reads for C'),
-              _expected_alt_based_call(['C', 'T'], 'seq for T', 'reads for T'),
+              _expected_alt_based_call(['C', 'T'], seq_for_c, 'reads for C'),
+              _expected_alt_based_call(['C', 'T'], seq_for_t, 'reads for T'),
           ],
           any_order=True)
 
+  def test_create_pileup_images_with_mismatched_alt_ref(self):
+    self.dv_call.variant.alternate_bases[:] = ['T']
+    # Deliberatly make the length different from self.pic.width.
+    haplotype_sequences = {'T': 'T' * (self.pic.width + 1)}
+    haplotype_alignments = {'T': 'reads for T'}
+    with mock.patch.object(
+        self.pic, 'build_pileup', autospec=True) as mock_encoder:
+      self.pic._options.alt_aligned_pileup = 'rows'
+      output = self.pic.create_pileup_images(
+          dv_call=self.dv_call,
+          reads_for_samples=self.reads_for_samples,
+          haplotype_alignments_for_samples=[haplotype_alignments],
+          haplotype_sequences=haplotype_sequences)
+      self.assertIsNone(output)
+      self.assertEqual(mock_encoder.call_count, 1)
+
   @parameterized.parameters(
       ((100, 221, 6), 'rows', (300, 221, 6)),
       ((100, 221, 6), 'base_channels', (100, 221, 8)),