diff --git a/splitter/simple/impl.go b/splitter/simple/impl.go
index 11fd0e9..fea1db2 100644
--- a/splitter/simple/impl.go
+++ b/splitter/simple/impl.go
@@ -315,6 +315,9 @@ func (m *SimpleMapper) OnJob(job proxy.Job) {
 	}
 	m.mu.Lock()
 	m.prevJob = m.currentJob
+	if m.prevJob.ClientID != job.ClientID {
+		m.prevJob = proxy.Job{}
+	}
 	m.currentJob = job
 	m.stopped = false
 	m.idleAt = time.Time{}
diff --git a/splitter/simple/impl_test.go b/splitter/simple/impl_test.go
index 2f47e44..e703217 100644
--- a/splitter/simple/impl_test.go
+++ b/splitter/simple/impl_test.go
@@ -293,6 +293,37 @@ func TestSimpleMapper_OnResultAccepted_CustomDiffUsesEffectiveDifficulty(t *test
 	}
 }
 
+func TestSimpleMapper_OnJob_PreservesPreviousJobForSamePoolSession_Good(t *testing.T) {
+	mapper := &SimpleMapper{
+		currentJob: proxy.Job{JobID: "job-1", Blob: "blob-1", ClientID: "session-a"},
+	}
+
+	mapper.OnJob(proxy.Job{JobID: "job-2", Blob: "blob-2", ClientID: "session-a"})
+
+	if mapper.currentJob.JobID != "job-2" {
+		t.Fatalf("expected current job to roll forward, got %q", mapper.currentJob.JobID)
+	}
+	if mapper.prevJob.JobID != "job-1" {
+		t.Fatalf("expected previous job to remain available within one pool session, got %q", mapper.prevJob.JobID)
+	}
+}
+
+func TestSimpleMapper_OnJob_ResetsPreviousJobAcrossPoolSessions_Ugly(t *testing.T) {
+	mapper := &SimpleMapper{
+		currentJob: proxy.Job{JobID: "job-1", Blob: "blob-1", ClientID: "session-a"},
+		prevJob:    proxy.Job{JobID: "job-0", Blob: "blob-0", ClientID: "session-a"},
+	}
+
+	mapper.OnJob(proxy.Job{JobID: "job-2", Blob: "blob-2", ClientID: "session-b"})
+
+	if mapper.currentJob.JobID != "job-2" {
+		t.Fatalf("expected current job to advance after session change, got %q", mapper.currentJob.JobID)
+	}
+	if mapper.prevJob.JobID != "" {
+		t.Fatalf("expected previous job history to reset on new pool session, got %q", mapper.prevJob.JobID)
+	}
+}
+
 func TestSimpleMapper_Submit_InvalidJob_Good(t *testing.T) {
 	minerConn, clientConn := net.Pipe()
 	defer minerConn.Close()