diff --git a/browser/components/urlbar/UrlbarInput.jsm b/browser/components/urlbar/UrlbarInput.jsm
index ea2245f31c6c..2add12cc96f2 100644
--- a/browser/components/urlbar/UrlbarInput.jsm
+++ b/browser/components/urlbar/UrlbarInput.jsm
@@ -1233,29 +1233,18 @@ class UrlbarInput {
     if (this.getAttribute("pageproxystate") == "valid") {
       uri = this.window.gBrowser.currentURI;
     } else {
-      // We're dealing with an autocompleted value.
-      if (!this._resultForCurrentValue) {
-        throw new Error(
-          "UrlbarInput: Should have a UrlbarResult since " +
-            "pageproxystate != 'valid' and valueIsTyped == false"
-        );
-      }
-      let resultURL = this._resultForCurrentValue.payload.url;
-      if (!resultURL) {
-        return selectedVal;
-      }
-
+      // The value could be:
+      // 1. a trimmed url, set by selecting a result
+      // 2. a search string set by selecting a result
+      // 3. a url that was confirmed but didn't finish loading yet
+      // If it's an url the untrimmedValue should resolve to a valid URI,
+      // otherwise it's a search string that should be copied as-is.
       try {
-        uri = Services.uriFixup.createFixupURI(
-          resultURL,
-          Services.uriFixup.FIXUP_FLAG_NONE
-        );
-      } catch (e) {}
-      if (!uri) {
+        uri = Services.io.newURI(this._untrimmedValue);
+      } catch (ex) {
         return selectedVal;
       }
     }
-
     uri = this.makeURIReadable(uri);
 
     // If the entire URL is selected, just use the actual loaded URI,
diff --git a/browser/components/urlbar/tests/browser/browser.ini b/browser/components/urlbar/tests/browser/browser.ini
index 5ab804425a73..69b8f1755908 100644
--- a/browser/components/urlbar/tests/browser/browser.ini
+++ b/browser/components/urlbar/tests/browser/browser.ini
@@ -118,6 +118,9 @@ support-files =
   file_blank_but_not_blank.html
 [browser_urlbar_collapseOnChromeMousedown.js]
 [browser_urlbar_content_opener.js]
+[browser_urlbar_copy_during_load.js]
+support-files =
+  slow-page.sjs
 [browser_urlbar_display_selectedAction_Extensions.js]
 [browser_urlbar_empty_search.js]
 [browser_urlbar_event_telemetry.js]
diff --git a/browser/components/urlbar/tests/browser/browser_urlbar_copy_during_load.js b/browser/components/urlbar/tests/browser/browser_urlbar_copy_during_load.js
new file mode 100644
index 000000000000..b24cbe077d24
--- /dev/null
+++ b/browser/components/urlbar/tests/browser/browser_urlbar_copy_during_load.js
@@ -0,0 +1,51 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test that copying from the urlbar page works correctly after a result is
+// confirmed but takes a while to load.
+
+add_task(async function() {
+  const SLOW_PAGE =
+    getRootDirectory(gTestPath).replace(
+      "chrome://mochitests/content",
+      "http://www.example.com"
+    ) + "slow-page.sjs";
+
+  await BrowserTestUtils.withNewTab(gBrowser, async tab => {
+    gURLBar.focus();
+    gURLBar.value = SLOW_PAGE;
+    let promise = TestUtils.waitForCondition(
+      () => gURLBar.getAttribute("pageproxystate") == "invalid"
+    );
+    EventUtils.synthesizeKey("KEY_Enter");
+    info("wait for the initial conditions");
+    await promise;
+
+    info("Copy the whole url");
+    await SimpleTest.promiseClipboardChange(SLOW_PAGE, () => {
+      gURLBar.select();
+      goDoCommand("cmd_copy");
+    });
+
+    info("Copy the initial part of the url, as a different valid url");
+    await SimpleTest.promiseClipboardChange(
+      SLOW_PAGE.substring(0, SLOW_PAGE.indexOf("slow-page.sjs")),
+      () => {
+        gURLBar.selectionStart = 0;
+        gURLBar.selectionEnd = gURLBar.value.indexOf("slow-page.sjs");
+        goDoCommand("cmd_copy");
+      }
+    );
+
+    // This is apparently necessary to avoid a timeout on mochitest shutdown(!?)
+    let browserStoppedPromise = BrowserTestUtils.browserStopped(
+      gBrowser,
+      null,
+      true
+    );
+    BrowserStop();
+    await browserStoppedPromise;
+  });
+});
diff --git a/browser/components/urlbar/tests/browser/slow-page.sjs b/browser/components/urlbar/tests/browser/slow-page.sjs
index 2612de834550..ce9a7597445a 100644
--- a/browser/components/urlbar/tests/browser/slow-page.sjs
+++ b/browser/components/urlbar/tests/browser/slow-page.sjs
@@ -11,9 +11,13 @@ function handleRequest(request, response) {
   }
   response.processAsync();
   timer = Cc["@mozilla.org/timer;1"].createInstance(Ci.nsITimer);
-  timer.init(() => {
-    response.setHeader("Content-Type", "text/html", false);
-    response.write("<body>This was the slow load. You should never see this.</body>");
-    response.finish();
-  }, DELAY_MS, Ci.nsITimer.TYPE_ONE_SHOT);
+  timer.init(
+    () => {
+      response.setHeader("Content-Type", "text/html", false);
+      response.write("<body>This is a slow loading page.</body>");
+      response.finish();
+    },
+    DELAY_MS,
+    Ci.nsITimer.TYPE_ONE_SHOT
+  );
 }