diff --git a/buildbot_nix/buildbot_nix/build_trigger.py b/buildbot_nix/buildbot_nix/build_trigger.py
index 7857b0eab..a53511ec5 100644
--- a/buildbot_nix/buildbot_nix/build_trigger.py
+++ b/buildbot_nix/buildbot_nix/build_trigger.py
@@ -8,7 +8,13 @@
 from buildbot.plugins import steps, util
 from buildbot.process import buildstep
 from buildbot.process.properties import Properties
-from buildbot.process.results import ALL_RESULTS, SUCCESS, statusToString, worst_status
+from buildbot.process.results import (
+    ALL_RESULTS,
+    CANCELLED,
+    SUCCESS,
+    statusToString,
+    worst_status,
+)
 from buildbot.reporters.utils import getURLForBuild, getURLForBuildrequest
 from twisted.internet import defer
 
@@ -95,6 +101,7 @@ class SchedulingContext:
         scheduled: list[BuildTrigger.ScheduledJob]
         scheduler_log: StreamLog
         schedule_now: list[NixEvalJobSuccess]
+        seen_drvs: dict[str, str]  # Maps drvPath to attr name of first occurrence
 
     def __init__(
         self,
@@ -530,7 +537,18 @@ async def _schedule_ready_jobs(
     ) -> list[NixEvalJobSuccess]:
         """Schedule jobs that are ready to run. Returns list of skipped jobs."""
         skipped_jobs = []
-        for job in ctx.schedule_now:
+        for job in sorted(ctx.schedule_now, key=lambda j: j.attr):
+            # Check if we've already scheduled a build for this derivation (alias detection)
+            if job.drvPath in ctx.seen_drvs:
+                original_attr = ctx.seen_drvs[job.drvPath]
+                ctx.scheduler_log.addStdout(
+                    f"\t- {job.attr} (skipped, alias of {original_attr})\n"
+                )
+                skipped_jobs.append(job)
+                self._skipped_count += 1
+                continue
+            ctx.seen_drvs[job.drvPath] = job.attr
+
             schedule_result = self.schedule_success(build_props, job)
             if schedule_result is not None:
                 ctx.scheduler_log.addStdout(f"\t- {job.attr}\n")
@@ -573,7 +591,15 @@ async def _wait_and_process_completed(
             fireOnOneCallback=True,
             fireOnOneErrback=True,
         )
-        results, index = await self.wait_for_finish_deferred  # type: ignore[assignment]
+        try:
+            results, index = await self.wait_for_finish_deferred  # type: ignore[assignment]
+        except defer.FirstError as e:
+            # DeferredList wraps the actual error in FirstError
+            if isinstance(e.subFailure.value, defer.CancelledError):
+                ctx.scheduler_log.addStdout("Build was cancelled\n")
+                return CANCELLED
+            # Re-raise other errors
+            raise
 
         # Get the completed job
         scheduled_job = ctx.scheduled.pop(index)
@@ -715,6 +741,7 @@ async def run(self) -> int:
             scheduled=scheduled,
             schedule_now=[],
             scheduler_log=scheduler_log,
+            seen_drvs={},
         )
 
         # Main scheduling loop