diff --git a/cypress/integration/WardrobePage/Outfit saving.spec.js b/cypress/integration/WardrobePage/Outfit saving.spec.js
index 3dc36e0..3bf44ce 100644
--- a/cypress/integration/WardrobePage/Outfit saving.spec.js	
+++ b/cypress/integration/WardrobePage/Outfit saving.spec.js	
@@ -92,4 +92,42 @@ describe("WardrobePage: Outfit saving", () => {
     cy.reload();
     page.getOutfitPreview({ timeout: 20000 }).toMatchImageSnapshot();
   });
+
+  it("prompts before navigating away from unsaved changes", () => {
+    // Create stub methods to reject navigation confirmation prompts. We need
+    // `confirm` for react-router's client-side nav, and `before:unload` for
+    // the browser's built-in full-page nav prompts.
+    const confirmStub = cy.stub().returns(false);
+    cy.on("window:confirm", confirmStub);
+    const beforeUnloadStub = cy.stub();
+    cy.on("window:before:unload", beforeUnloadStub);
+
+    cy.logInAs("dti-test");
+    cy.visit("/outfits/new?species=1&color=8");
+
+    // Give the outfit a unique timestamped name
+    const outfitName = `Cypress Test - Block Navigation - ${new Date().toISOString()}`;
+    page.getOutfitName({ timeout: 12000 }).click();
+    cy.focused().type(outfitName + "{enter}");
+
+    // Save the outfit, but don't wait for it to finish.
+    page.getSaveOutfitButton().click().should("have.attr", "data-loading");
+
+    // Click the big back button, and observe that it triggers a confirm prompt.
+    // We'll reject it. HACK: It's a bit flaky if you try the clicks
+    // immediately in sequence. Is there a better way to do this?
+    page.showOutfitControls();
+    cy.wait(100); // eslint-disable-line cypress/no-unnecessary-waiting
+    page.getNavBackButton().click();
+    cy.wrap(confirmStub).should("be.called");
+
+    // Try to reload the page, and observe that it would trigger the browser's
+    // built-in prompt, i.e., `defaultPrevented`. Cypress will automatically
+    // confirm the simulated prompt, and complete the reload.
+    cy.reload();
+    cy.wrap(beforeUnloadStub).should(
+      "be.calledWith",
+      Cypress.sinon.match((e) => e.defaultPrevented)
+    );
+  });
 });
diff --git a/cypress/integration/WardrobePage/page.js b/cypress/integration/WardrobePage/page.js
index 624f533..2a6bf15 100644
--- a/cypress/integration/WardrobePage/page.js
+++ b/cypress/integration/WardrobePage/page.js
@@ -1,6 +1,7 @@
 const withTestId = (testId) => (options) =>
   cy.get(`[data-test-id="${CSS.escape(testId)}"]`, options);
 
+export const getNavBackButton = withTestId("wardrobe-nav-back-button");
 export const getSpeciesSelect = withTestId("wardrobe-species-picker");
 export const getColorSelect = withTestId("wardrobe-color-picker");
 export const getPosePickerButton = withTestId("wardrobe-pose-picker");
@@ -38,3 +39,7 @@ export function getOutfitPreview(options = { timeout: 15000 }) {
     .get("img")
     .first();
 }
+
+export function showOutfitControls(options) {
+  return cy.get("[data-test-id=wardrobe-outfit-controls]", options).click();
+}
diff --git a/src/app/WardrobePage/OutfitControls.js b/src/app/WardrobePage/OutfitControls.js
index ecfe67d..75fe9c9 100644
--- a/src/app/WardrobePage/OutfitControls.js
+++ b/src/app/WardrobePage/OutfitControls.js
@@ -146,6 +146,7 @@ function OutfitControls({
               setFocusIsLocked(true);
             }
           }}
+          data-test-id="wardrobe-outfit-controls"
         >
           <Box gridArea="back" onClick={maybeUnlockFocus}>
             <BackButton outfitState={outfitState} />
@@ -297,6 +298,7 @@ function BackButton({ outfitState }) {
       icon={<ArrowBackIcon />}
       aria-label="Leave this outfit"
       d="inline-flex" // Not sure why <a> requires this to style right! ^^`
+      data-test-id="wardrobe-nav-back-button"
     />
   );
 }
diff --git a/src/app/WardrobePage/index.js b/src/app/WardrobePage/index.js
index f01acf9..561e06f 100644
--- a/src/app/WardrobePage/index.js
+++ b/src/app/WardrobePage/index.js
@@ -1,4 +1,5 @@
 import React from "react";
+import { Prompt } from "react-router-dom";
 import { useToast } from "@chakra-ui/react";
 import { loadable } from "../util";
 
@@ -29,7 +30,8 @@ function WardrobePage() {
 
   // We manage outfit saving up here, rather than at the point of the UI where
   // "Saving" indicators appear. That way, auto-saving still happens even when
-  // the indicator isn't on the page, e.g. when searching.
+  // the indicator isn't on the page, e.g. when searching. We also mount a
+  // <Prompt /> in this component to prevent navigating away before saving.
   const outfitSaving = useOutfitSaving(outfitState, dispatchToOutfit);
 
   usePageTitle(outfitState.name || "Untitled outfit");
@@ -49,6 +51,27 @@ function WardrobePage() {
     }
   }, [error, toast]);
 
+  // For new outfits, we only block navigation while saving. For existing
+  // outfits, we block navigation while there are any unsaved changes.
+  const shouldBlockNavigation =
+    outfitSaving.canSaveOutfit &&
+    ((outfitSaving.isNewOutfit && outfitSaving.isSaving) ||
+      (!outfitSaving.isNewOutfit && !outfitSaving.latestVersionIsSaved));
+
+  // In addition to a <Prompt /> for client-side nav, we need to block full nav!
+  React.useEffect(() => {
+    if (shouldBlockNavigation) {
+      const onBeforeUnload = (e) => {
+        // https://developer.mozilla.org/en-US/docs/Web/API/WindowEventHandlers/onbeforeunload#example
+        e.preventDefault();
+        e.returnValue = "";
+      };
+
+      window.addEventListener("beforeunload", onBeforeUnload);
+      return () => window.removeEventListener("beforeunload", onBeforeUnload);
+    }
+  }, [shouldBlockNavigation]);
+
   // NOTE: Most components pass around outfitState directly, to make the data
   //       relationships more explicit... but there are some deep components
   //       that need it, where it's more useful and more performant to access
@@ -58,6 +81,21 @@ function WardrobePage() {
       <SupportOnly>
         <WardrobeDevHacks />
       </SupportOnly>
+
+      {/*
+       * TODO: This might unnecessarily block navigations that we don't
+       * necessarily need to, e.g., navigating back to Your Outfits while the
+       * save request is in flight. We could instead submit the save mutation
+       * immediately on client-side nav, and have each outfit save mutation
+       * install a `beforeunload` handler that ensures that you don't close
+       * the page altogether while it's in flight. But let's start simple and
+       * see how annoying it actually is in practice lol
+       */}
+      <Prompt
+        when={shouldBlockNavigation}
+        message="Are you sure you want to leave? Your changes might not be saved."
+      />
+
       <WardrobePageLayout
         previewAndControls={
           <WardrobePreviewAndControls