diff --git a/src/main/kotlin/de/joshavg/BuildsEndpoint.kt b/src/main/kotlin/de/joshavg/BuildsEndpoint.kt
index bee047a..a35e310 100644
--- a/src/main/kotlin/de/joshavg/BuildsEndpoint.kt
+++ b/src/main/kotlin/de/joshavg/BuildsEndpoint.kt
@@ -7,6 +7,7 @@ import javax.inject.Inject
 import javax.ws.rs.*
 import javax.ws.rs.core.MediaType
 import javax.ws.rs.core.Response
+import javax.ws.rs.core.Response.Status.PRECONDITION_REQUIRED
 
 @Path("/builds")
 class BuildsEndpoint(
@@ -35,19 +36,24 @@ class BuildsEndpoint(
     fun trigger(@PathParam("build")
                 build: String,
                 @QueryParam("key")
-                key: String?) =
+                key: String?,
+                @QueryParam("rev")
+                rev: String?) =
         security.requireKey(build, key) {
             val logFile = builds.createLogFile(build)
 
-            startBuildThread(build, logFile, it)
+            if (rev == null) {
+                return@requireKey Response.status(PRECONDITION_REQUIRED).build()
+            }
+
+            startBuildThread(build, rev, logFile, it)
 
             Response.ok(mapOf(
                 "log" to logFile.absolutePath
-            ))
-                .build()
+            )).build()
         }
 
-    fun startBuildThread(build: String, logFile: File, config: BuildConfig) =
+    fun startBuildThread(build: String, rev: String, logFile: File, config: BuildConfig) =
         Thread {
             logger.info("preparing process for build $build with config ${config.asPublic()}")
             logger.info("log file: $logFile")
@@ -59,6 +65,7 @@ class BuildsEndpoint(
                 .apply {
                     environment().putAll(config.env)
                     environment()["ALFRED_LOG_FILE"] = logFile.absolutePath
+                    environment()["ALFRED_GIT_REV"] = rev
                 }
                 .start()
                 .toHandle()