diff --git a/docs/install/installing-istio.md b/docs/install/installing-istio.md
index eceb43ddfda..3cecc4a740b 100644
--- a/docs/install/installing-istio.md
+++ b/docs/install/installing-istio.md
@@ -18,7 +18,13 @@ instructions.
 You need:
 
 - A Kubernetes cluster created.
-- [`istioctl`](https://istio.io/docs/setup/install/istioctl/) (v1.5.4 or later) installed.
+- [`istioctl`](https://istio.io/docs/setup/install/istioctl/) (v1.4.10 or later) installed.
+
+## Supported Istio versions
+
+The current known-to-be-stable version of Istio tested in conjunction with Knative is **v1.4.10**.
+Versions in the 1.4 line generally be fine too.
+Versions above the 1.4 line are under test but have not stabilized yet.
 
 ## Installing Istio