diff --git a/src/popup/index.js b/src/popup/index.js
index 5c98a60..429ea5e 100644
--- a/src/popup/index.js
+++ b/src/popup/index.js
@@ -2,7 +2,12 @@
 // Loads state, initializes views, triggers first render.
 
 const { DEBUG } = require("../shared/constants");
-const { state, saveState, loadState } = require("../shared/state");
+const {
+    state,
+    saveState,
+    loadState,
+    currentNetwork,
+} = require("../shared/state");
 const { refreshPrices } = require("../shared/prices");
 const { refreshBalances } = require("../shared/balances");
 const { $, showView } = require("./views/helpers");
@@ -167,12 +172,24 @@ function fallbackView() {
 }
 
 async function init() {
-    if (DEBUG) {
+    const net = currentNetwork();
+    if (DEBUG || net.isTestnet) {
         const banner = document.createElement("div");
         banner.id = "debug-banner";
-        banner.textContent = "DEBUG / INSECURE";
         banner.style.cssText =
-            "background:#c00;color:#fff;text-align:center;font-size:10px;padding:1px 0;font-family:monospace;position:sticky;top:0;z-index:9999;";
+            "background:#c00;color:#fff;text-align:center;font-size:10px;padding:1px 0;font-family:monospace;position:sticky;top:0;z-index:9999;display:flex;justify-content:center;align-items:center;";
+        const label = document.createElement("span");
+        label.id = "debug-banner-label";
+        label.style.cssText = "flex:1;text-align:center;";
+        label.textContent = DEBUG ? "DEBUG / INSECURE" : net.name;
+        banner.appendChild(label);
+        if (net.isTestnet) {
+            const tag = document.createElement("span");
+            tag.id = "debug-banner-testnet";
+            tag.style.cssText = "position:absolute;right:6px;font-weight:bold;";
+            tag.textContent = "TESTNET";
+            banner.appendChild(tag);
+        }
         document.body.prepend(banner);
     }
 
diff --git a/src/popup/views/helpers.js b/src/popup/views/helpers.js
index 450c98e..e0472bf 100644
--- a/src/popup/views/helpers.js
+++ b/src/popup/views/helpers.js
@@ -6,7 +6,7 @@ const {
     getPrice,
     getAddressValueUsd,
 } = require("../../shared/prices");
-const { state, saveState } = require("../../shared/state");
+const { state, saveState, currentNetwork } = require("../../shared/state");
 
 // When views are added, removed, or transitions between them change,
 // update the view-navigation documentation in README.md to match.
@@ -59,10 +59,13 @@ function showView(name) {
     clearFlash();
     state.currentView = name;
     saveState();
-    if (DEBUG) {
-        const banner = document.getElementById("debug-banner");
-        if (banner) {
-            banner.textContent = "DEBUG / INSECURE (" + name + ")";
+    const net = currentNetwork();
+    if (DEBUG || net.isTestnet) {
+        const label = document.getElementById("debug-banner-label");
+        if (label) {
+            label.textContent = DEBUG
+                ? "DEBUG / INSECURE (" + name + ")"
+                : net.name + " (" + name + ")";
         }
     }
 }