diff --git a/app/vmalert/datasource/vm_prom_api.go b/app/vmalert/datasource/vm_prom_api.go
index 5e80cb820..1b5fd5915 100644
--- a/app/vmalert/datasource/vm_prom_api.go
+++ b/app/vmalert/datasource/vm_prom_api.go
@@ -149,6 +149,16 @@ func (s *VMStorage) setPrometheusInstantReqParams(r *http.Request, query string,
 		timestamp = timestamp.Truncate(s.evaluationInterval)
 	}
 	q.Set("time", fmt.Sprintf("%d", timestamp.Unix()))
+	if s.evaluationInterval > 0 { // set step as evaluationInterval by default
+		// always convert to seconds to keep compatibility with older
+		// Prometheus versions. See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1943
+		q.Set("step", fmt.Sprintf("%ds", int(s.evaluationInterval.Seconds())))
+	}
+	if s.queryStep > 0 { // override step with user-specified value
+		// always convert to seconds to keep compatibility with older
+		// Prometheus versions. See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1943
+		q.Set("step", fmt.Sprintf("%ds", int(s.queryStep.Seconds())))
+	}
 	r.URL.RawQuery = q.Encode()
 	s.setPrometheusReqParams(r, query)
 }
@@ -163,6 +173,11 @@ func (s *VMStorage) setPrometheusRangeReqParams(r *http.Request, query string, s
 	q := r.URL.Query()
 	q.Add("start", fmt.Sprintf("%d", start.Unix()))
 	q.Add("end", fmt.Sprintf("%d", end.Unix()))
+	if s.evaluationInterval > 0 { // set step as evaluationInterval by default
+		// always convert to seconds to keep compatibility with older
+		// Prometheus versions. See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1943
+		q.Set("step", fmt.Sprintf("%ds", int(s.evaluationInterval.Seconds())))
+	}
 	r.URL.RawQuery = q.Encode()
 	s.setPrometheusReqParams(r, query)
 }
@@ -178,15 +193,5 @@ func (s *VMStorage) setPrometheusReqParams(r *http.Request, query string) {
 		}
 	}
 	q.Set("query", query)
-	if s.evaluationInterval > 0 { // set step as evaluationInterval by default
-		// always convert to seconds to keep compatibility with older
-		// Prometheus versions. See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1943
-		q.Set("step", fmt.Sprintf("%ds", int(s.evaluationInterval.Seconds())))
-	}
-	if s.queryStep > 0 { // override step with user-specified value
-		// always convert to seconds to keep compatibility with older
-		// Prometheus versions. See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1943
-		q.Set("step", fmt.Sprintf("%ds", int(s.queryStep.Seconds())))
-	}
 	r.URL.RawQuery = q.Encode()
 }
diff --git a/app/vmalert/datasource/vm_test.go b/app/vmalert/datasource/vm_test.go
index 1cd433cee..f993dc2c9 100644
--- a/app/vmalert/datasource/vm_test.go
+++ b/app/vmalert/datasource/vm_test.go
@@ -197,6 +197,10 @@ func TestVMRangeQuery(t *testing.T) {
 		if _, err := strconv.ParseInt(endTS, 10, 64); err != nil {
 			t.Errorf("failed to parse 'end' query param: %s", err)
 		}
+		step := r.URL.Query().Get("step")
+		if step != "15s" {
+			t.Errorf("expected 'step' query param to be 15s; got %q instead", step)
+		}
 		switch c {
 		case 0:
 			w.Write([]byte(`{"status":"success","data":{"resultType":"matrix","result":[{"metric":{"__name__":"vm_rows"},"values":[[1583786142,"13763"]]}]}}`))
@@ -210,7 +214,7 @@ func TestVMRangeQuery(t *testing.T) {
 	if err != nil {
 		t.Fatalf("unexpected: %s", err)
 	}
-	s := NewVMStorage(srv.URL, authCfg, time.Minute, 0, false, srv.Client())
+	s := NewVMStorage(srv.URL, authCfg, time.Minute, *queryStep, false, srv.Client())
 
 	p := NewPrometheusType()
 	pq := s.BuildWithParams(QuerierParams{DataSourceType: &p, EvaluationInterval: 15 * time.Second})
diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index 9156af45f..c151515f7 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -15,6 +15,7 @@ The following tip changes can be tested by building VictoriaMetrics components f
 
 ## v1.79.x long-time support release (LTS)
 
+* BUGFIX: [vmalert](https://docs.victoriametrics.com/vmalert.html): properly specify rule evaluation step during the [replay mode](https://docs.victoriametrics.com/vmalert.html#rules-backfilling). The `step` value was previously overriden by `datasource.queryStep` flag.
 * BUGFIX: [vmalert](https://docs.victoriametrics.com/vmalert.html): properly return the error message from remote-write failures. Before, error was ignored and only `vmalert_remotewrite_errors_total` was incremented.
 * BUGFIX: [MetricsQL](https://docs.victoriametrics.com/MetricsQL.html): properly return an empty result from [limit_offset](https://docs.victoriametrics.com/MetricsQL.html#limit_offset) if the `offset` arg exceeds the number of inner time series. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3312).
 * BUGFIX: [vmagent](https://docs.victoriametrics.com/vmagent.html): properly discover GCE zones when `filter` option is set at [gce_sd_configs](https://docs.victoriametrics.com/sd_configs.html#gce_sd_configs). See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3202).