diff --git a/elasticsearch/src/main/java/org/elasticsearch/xpack/prelert/job/Job.java b/elasticsearch/src/main/java/org/elasticsearch/xpack/prelert/job/Job.java
index 3454cd9559c..39cc2bd4285 100644
--- a/elasticsearch/src/main/java/org/elasticsearch/xpack/prelert/job/Job.java
+++ b/elasticsearch/src/main/java/org/elasticsearch/xpack/prelert/job/Job.java
@@ -693,7 +693,16 @@ public class Job extends AbstractDiffable<Job> implements Writeable, ToXContent
             Date lastDataTime;
             String modelSnapshotId;
             if (fromApi) {
-                id = this.id == null ? UUIDs.base64UUID().toLowerCase(Locale.ROOT): this.id;
+                if (this.id != null) {
+                    id = this.id;
+                } else {
+                    // Base64 UUIDs are not necessarily valid job IDs
+                    id = "auto-" + UUIDs.base64UUID().toLowerCase(Locale.ROOT).replaceAll("/\\+=", "_");
+                    if (id.endsWith("_")) {
+                        // Job IDs cannot end with underscores
+                        id = id.substring(0, id.length() - 1) + "z";
+                    }
+                }
                 createTime = this.createTime == null ? new Date() : this.createTime;
                 finishedTime = null;
                 lastDataTime = null;
diff --git a/elasticsearch/src/test/java/org/elasticsearch/xpack/prelert/job/JobTests.java b/elasticsearch/src/test/java/org/elasticsearch/xpack/prelert/job/JobTests.java
index 54af4355c95..434021f3c05 100644
--- a/elasticsearch/src/test/java/org/elasticsearch/xpack/prelert/job/JobTests.java
+++ b/elasticsearch/src/test/java/org/elasticsearch/xpack/prelert/job/JobTests.java
@@ -82,6 +82,12 @@ public class JobTests extends AbstractSerializingTestCase<Job> {
         assertNotNull(buildJobBuilder(null).build(true).getId()); // test auto id generation
     }
 
+    public void testNoIdStartsWithAuto() {
+        String autoId = buildJobBuilder(null).build(true).getId();
+        assertTrue(autoId, autoId.startsWith("auto-"));
+        assertFalse(autoId, autoId.endsWith("_"));
+    }
+
     public void testEquals_GivenDifferentClass() {
         Job job = buildJobBuilder("foo").build();
         assertFalse(job.equals("a string"));