--- a/bitten/model.py
+++ b/bitten/model.py
@@ -341,7 +341,7 @@
             Column('rev_time', type='int'), Column('platform', type='int'),
             Column('slave'), Column('started', type='int'),
             Column('stopped', type='int'), Column('status', size=1),
-            Index(['config', 'rev', 'slave'])
+            Index(['config', 'rev', 'platform'], unique=True)
         ],
         Table('bitten_slave', key=('build', 'propname'))[
             Column('build', type='int'), Column('propname'), Column('propvalue')
@@ -998,4 +998,4 @@
 
 schema = BuildConfig._schema + TargetPlatform._schema + Build._schema + \
          BuildStep._schema + BuildLog._schema + Report._schema
-schema_version = 9
+schema_version = 10

--- a/bitten/queue.py
+++ b/bitten/queue.py
@@ -246,9 +246,17 @@
                     builds.append(build)
 
         for build in builds:
-            build.insert(db=db)
-
-        db.commit()
+            try:
+                build.insert(db=db)
+                db.commit()
+            except Exception, e:
+                # really only want to catch IntegrityErrors raised when
+                # a second slave attempts to add builds with the same
+                # (config, platform, rev) as an existing build.
+                self.log.info('Failed to insert build of configuration "%s" '
+                    'at revision [%s] on platform [%s]: %s',
+                    build.config, build.rev, build.platform, e)
+                db.rollback()
 
     def reset_orphaned_builds(self):
         """Reset all in-progress builds to ``PENDING`` state if they've been

--- a/bitten/tests/queue.py
+++ b/bitten/tests/queue.py
@@ -11,6 +11,7 @@
 import os
 import shutil
 import tempfile
+import threading
 import time
 import unittest
 
@@ -261,6 +262,63 @@
         self.assertEqual(platform2.id, builds[5].platform)
         self.assertEqual('120', builds[5].rev)
 
+    def test_populate_thread_race_condition(self):
+        messages = []
+        self.env.log = Mock(info=lambda msg, *args: messages.append(msg))
+        def get_history():
+            yield ('somepath', 123, 'edit')
+            yield ('somepath', 121, 'edit')
+            yield ('somepath', 120, 'edit')
+            time.sleep(1) # sleep to make sure both threads collect
+        self.env.get_repository = lambda authname=None: Mock(
+            get_changeset=lambda rev: Mock(date=to_datetime(rev * 1000, utc)),
+            get_node=lambda path, rev=None: Mock(
+                get_entries=lambda: [Mock(), Mock()],
+                get_history=get_history
+            ),
+            normalize_path=lambda path: path,
+            rev_older_than=lambda rev1, rev2: rev1 < rev2
+        )
+        BuildConfig(self.env, 'test', path='somepath', active=True).insert()
+        platform1 = TargetPlatform(self.env, config='test', name='P1')
+        platform1.insert()
+        platform2 = TargetPlatform(self.env, config='test', name='P2')
+        platform2.insert()
+
+        class BuildPopulator(threading.Thread):
+            def __init__(self, env):
+                self.env = env
+                threading.Thread.__init__(self)
+            def run(self):
+                queue = BuildQueue(self.env, build_all=True)
+                queue.populate()
+        
+        thread1 = BuildPopulator(self.env)
+        thread2 = BuildPopulator(self.env)
+        thread1.start(); thread2.start()
+        thread1.join(); thread2.join()
+
+        # check builds got added
+        builds = list(Build.select(self.env, config='test'))
+        builds.sort(lambda a, b: cmp(a.platform, b.platform))
+        self.assertEqual(6, len(builds))
+        self.assertEqual(platform1.id, builds[0].platform)
+        self.assertEqual('123', builds[0].rev)
+        self.assertEqual(platform1.id, builds[1].platform)
+        self.assertEqual('121', builds[1].rev)
+        self.assertEqual(platform1.id, builds[2].platform)
+        self.assertEqual('120', builds[2].rev)
+        self.assertEqual(platform2.id, builds[3].platform)
+        self.assertEqual('123', builds[3].rev)
+        self.assertEqual(platform2.id, builds[4].platform)
+        self.assertEqual('121', builds[4].rev)
+        self.assertEqual(platform2.id, builds[5].platform)
+        self.assertEqual('120', builds[5].rev)
+
+        # check attempts at duplicate inserts were logged.
+        failure_messages = [x for x in messages if x.startswith('Failed to insert build')]
+        self.assertEqual(6, len(failure_messages))
+
     def test_should_delete_build_platform_dont_exist(self):
         messages = []
         self.env.log = Mock(info=lambda msg, *args: messages.append(msg))

--- a/bitten/upgrades.py
+++ b/bitten/upgrades.py
@@ -358,6 +358,12 @@
                     cursor.execute(stmt)
                 cursor.execute("INSERT INTO bitten_rule (id,propname,pattern,orderno) SELECT %s,propname,pattern,orderno FROM old_rule" % db.cast('id', 'int'))
 
+def add_config_platform_rev_index_to_build(env, db):
+    """Adds a unique index on (config, platform, rev) to the bitten_build table.
+       Also drops the old index on bitten_build that serves no real purpose anymore."""
+    cursor = db.cursor()
+    cursor.execute("CREATE UNIQUE INDEX bitten_build_config_rev_platform_idx ON bitten_build (config,rev,platform)")
+    cursor.execute("DROP INDEX bitten_build_config_rev_slave_idx")
 
 map = {
     2: [add_log_table],
@@ -368,4 +374,5 @@
     7: [add_error_table],
     8: [add_filename_to_logs,migrate_logs_to_files],
     9: [recreate_rule_with_int_id],
+   10: [add_config_platform_rev_index_to_build],
 }