diff --git a/pkg/cluster/majorversionupgrade.go b/pkg/cluster/majorversionupgrade.go
index 11064e342..ecf99c610 100644
--- a/pkg/cluster/majorversionupgrade.go
+++ b/pkg/cluster/majorversionupgrade.go
@@ -1,8 +1,6 @@
 package cluster
 
 import (
-	"fmt"
-
 	"github.com/zalando/postgres-operator/pkg/spec"
 	v1 "k8s.io/api/core/v1"
 )
@@ -80,8 +78,7 @@ func (c *Cluster) majorVersionUpgrade() error {
 		if c.currentMajorVersion < desiredVersion {
 			podName := &spec.NamespacedName{Namespace: masterPod.Namespace, Name: masterPod.Name}
 			c.logger.Infof("triggering major version upgrade on pod %s of %d pods", masterPod.Name, numberOfPods)
-			command := fmt.Sprintf("/bin/su postgres -c \"/usr/bin/python3 /scripts/inplace_upgrade.py %d 2>&1 | tee last_upgrade.log\"", numberOfPods)
-			_, err := c.ExecCommand(podName, command)
+			_, err := c.ExecCommand(podName, "/bin/su", "postgres", "-c", "\"/usr/bin/python3 /scripts/inplace_upgrade.py %d 2>&1 | tee last_upgrade.log\"")
 			if err != nil {
 				return err
 			}