diff --git a/tools/releasetools/common.py b/tools/releasetools/common.py
index 5e70af1..0683678 100644
--- a/tools/releasetools/common.py
+++ b/tools/releasetools/common.py
@@ -1085,6 +1085,38 @@
   return merged_dict
 
 
+def SharedUidPartitionViolations(uid_dict, partition_groups):
+  """Checks for APK sharedUserIds that cross partition group boundaries.
+
+  This uses a single or merged build's shareduid_violation_modules.json
+  output file, as generated by find_shareduid_violation.py or
+  core/tasks/find-shareduid-violation.mk.
+
+  An error is defined as a sharedUserId that is found in a set of partitions
+  that span more than one partition group.
+
+  Args:
+    uid_dict: A dictionary created by using the standard json module to read a
+      complete shareduid_violation_modules.json file.
+    partition_groups: A list of groups, where each group is a list of
+      partitions.
+
+  Returns:
+    A list of error messages.
+  """
+  errors = []
+  for uid, partitions in uid_dict.items():
+    found_in_groups = [
+        group for group in partition_groups
+        if set(partitions.keys()) & set(group)
+    ]
+    if len(found_in_groups) > 1:
+      errors.append(
+          "APK sharedUserId \"%s\" found across partition groups in partitions \"%s\""
+          % (uid, ",".join(sorted(partitions.keys()))))
+  return errors
+
+
 def AppendAVBSigningArgs(cmd, partition):
   """Append signing arguments for avbtool."""
   # e.g., "--key path/to/signing_key --algorithm SHA256_RSA4096"
diff --git a/tools/releasetools/merge_target_files.py b/tools/releasetools/merge_target_files.py
index 0d135d6..ba9e740 100755
--- a/tools/releasetools/merge_target_files.py
+++ b/tools/releasetools/merge_target_files.py
@@ -85,6 +85,7 @@
 from __future__ import print_function
 
 import fnmatch
+import json
 import logging
 import os
 import re
@@ -944,20 +945,32 @@
   if not check_target_files_vintf.CheckVintf(output_target_files_temp_dir):
     raise RuntimeError('Incompatible VINTF metadata')
 
+  # Generate and check for cross-partition violations of sharedUserId
+  # values in APKs. This requires the input target-files packages to contain
+  # *.apk files.
   shareduid_violation_modules = os.path.join(
       output_target_files_temp_dir, 'META', 'shareduid_violation_modules.json')
   with open(shareduid_violation_modules, 'w') as f:
-    partition_map = {
-        'system': 'SYSTEM',
-        'vendor': 'VENDOR',
-        'product': 'PRODUCT',
-        'system_ext': 'SYSTEM_EXT',
-    }
+    framework_partitions = item_list_to_partition_set(framework_item_list)
+    vendor_partitions = item_list_to_partition_set(vendor_item_list)
+
+    partition_map = {}
+    for partition in (framework_partitions.union(vendor_partitions)):
+      partition_map[partition.lower()] = partition.upper()
     violation = find_shareduid_violation.FindShareduidViolation(
         output_target_files_temp_dir, partition_map)
+
+    # Write the output to a file to enable debugging.
     f.write(violation)
-    # TODO(b/171431774): Add a check to common.py to check if the
-    # shared UIDs cross the input build partition boundary.
+
+    # Check for violations across the input builds' partition groups.
+    shareduid_errors = common.SharedUidPartitionViolations(
+        json.loads(violation), [framework_partitions, vendor_partitions])
+    if shareduid_errors:
+      for error in shareduid_errors:
+        logger.error(error)
+      raise ValueError('sharedUserId APK error. See %s' %
+                       shareduid_violation_modules)
 
   generate_images(output_target_files_temp_dir, rebuild_recovery)
 
diff --git a/tools/releasetools/test_common.py b/tools/releasetools/test_common.py
index ee28571..0b368f9 100644
--- a/tools/releasetools/test_common.py
+++ b/tools/releasetools/test_common.py
@@ -15,6 +15,7 @@
 #
 
 import copy
+import json
 import os
 import subprocess
 import tempfile
@@ -995,6 +996,34 @@
         },
         sparse_image.file_map)
 
+  def test_SharedUidPartitionViolations(self):
+    uid_dict = {
+        'android.uid.phone': {
+            'system': ['system_phone.apk'],
+            'system_ext': ['system_ext_phone.apk'],
+        },
+        'android.uid.wifi': {
+            'vendor': ['vendor_wifi.apk'],
+            'odm': ['odm_wifi.apk'],
+        },
+    }
+    errors = common.SharedUidPartitionViolations(
+        uid_dict, [('system', 'system_ext'), ('vendor', 'odm')])
+    self.assertEqual(errors, [])
+
+  def test_SharedUidPartitionViolations_Violation(self):
+    uid_dict = {
+        'android.uid.phone': {
+            'system': ['system_phone.apk'],
+            'vendor': ['vendor_phone.apk'],
+        },
+    }
+    errors = common.SharedUidPartitionViolations(
+        uid_dict, [('system', 'system_ext'), ('vendor', 'odm')])
+    self.assertIn(
+        ('APK sharedUserId "android.uid.phone" found across partition groups '
+         'in partitions "system,vendor"'), errors)
+
   def test_GetSparseImage_missingImageFile(self):
     self.assertRaises(
         AssertionError, common.GetSparseImage, 'system2', self.testdata_dir,