diff --git a/api/internal/endpointutils/endpointutils.go b/api/internal/endpointutils/endpointutils.go
index ca9f34ad1..68120355b 100644
--- a/api/internal/endpointutils/endpointutils.go
+++ b/api/internal/endpointutils/endpointutils.go
@@ -234,7 +234,7 @@ func getEndpointCheckinInterval(endpoint *portainer.Endpoint, settings *portaine
 		{endpoint.Edge.SnapshotInterval, settings.Edge.SnapshotInterval},
 	}
 
-	for i := range len(intervals) {
+	for i := range intervals {
 		effectiveInterval := intervals[i][0]
 		if effectiveInterval <= 0 {
 			effectiveInterval = intervals[i][1]
diff --git a/api/internal/upgrade/upgrade_docker.go b/api/internal/upgrade/upgrade_docker.go
index f7f4ecc59..7f5a24528 100644
--- a/api/internal/upgrade/upgrade_docker.go
+++ b/api/internal/upgrade/upgrade_docker.go
@@ -36,10 +36,12 @@ func (service *service) upgradeDocker(environment *portainer.Endpoint, licenseKe
 		return err
 	}
 
+	updaterImage := getUpdaterImage()
+
 	composeFile, err := mustache.RenderFile(templateName, map[string]string{
 		"image":           image,
 		"skip_pull_image": skipPullImageEnv,
-		"updater_image":   os.Getenv(updaterImageEnvVar),
+		"updater_image":   updaterImage,
 		"license":         licenseKey,
 		"envType":         envType,
 	})
@@ -115,3 +117,11 @@ func (service *service) checkImageForDocker(ctx context.Context, environment *po
 		return nil
 	}
 }
+
+func getUpdaterImage() string {
+	updaterImage := os.Getenv(updaterImageEnvVar)
+	if updaterImage == "" {
+		updaterImage = "portainer/portainer-updater:" + portainer.APIVersion
+	}
+	return updaterImage
+}
diff --git a/api/internal/upgrade/upgrade_docker_test.go b/api/internal/upgrade/upgrade_docker_test.go
new file mode 100644
index 000000000..f14d16ea3
--- /dev/null
+++ b/api/internal/upgrade/upgrade_docker_test.go
@@ -0,0 +1,29 @@
+package upgrade
+
+import (
+	"os"
+	"testing"
+
+	portainer "github.com/portainer/portainer/api"
+)
+
+func TestGetUpdaterImage(t *testing.T) {
+	t.Run("updater image Environment Variable is set", func(t *testing.T) {
+		os.Setenv(updaterImageEnvVar, "portainer/portainer-updater:pr111")
+
+		expect := "portainer/portainer-updater:pr111"
+		updaterImage := getUpdaterImage()
+		if updaterImage != expect {
+			t.Fatalf("expected %v, got %v", expect, updaterImage)
+		}
+	})
+
+	t.Run("updater image Environment Variable not set", func(t *testing.T) {
+		os.Unsetenv(updaterImageEnvVar)
+		expect := "portainer/portainer-updater:" + portainer.APIVersion
+		updaterImage := getUpdaterImage()
+		if updaterImage != expect {
+			t.Fatalf("expected %v, got %v", expect, updaterImage)
+		}
+	})
+}