diff --git a/dom/base/ResponsiveImageSelector.cpp b/dom/base/ResponsiveImageSelector.cpp
index 13f7f1867305..888077d505cf 100644
--- a/dom/base/ResponsiveImageSelector.cpp
+++ b/dom/base/ResponsiveImageSelector.cpp
@@ -39,8 +39,7 @@ ParseInteger(const nsAString& aString, int32_t& aInt)
   return !(parseResult &
            ( nsContentUtils::eParseHTMLInteger_Error |
              nsContentUtils::eParseHTMLInteger_DidNotConsumeAllInput |
-             nsContentUtils::eParseHTMLInteger_IsPercent |
-             nsContentUtils::eParseHTMLInteger_NonStandard ));
+             nsContentUtils::eParseHTMLInteger_IsPercent ));
 }
 
 ResponsiveImageSelector::ResponsiveImageSelector(nsIContent *aContent)
@@ -621,13 +620,11 @@ ResponsiveImageCandidate::ConsumeDescriptors(nsAString::const_iterator& aIter,
         // End of current descriptor, consume it, skip spaces
         // ("After descriptor" state in spec) before continuing
         descriptors.AddDescriptor(Substring(currentDescriptor, iter));
-        for (; iter != end && nsContentUtils::IsHTMLWhitespace(*iter); ++iter);
+        for (; iter != end && *iter == char16_t(' '); ++iter);
         if (iter == end) {
           break;
         }
         currentDescriptor = iter;
-        // Leave one whitespace so the loop advances to this position next iteration
-        iter--;
       } else if (*iter == char16_t('(')) {
         inParens = true;
       }
diff --git a/dom/tests/mochitest/general/test_img_mutations.html b/dom/tests/mochitest/general/test_img_mutations.html
index e2bc72d86416..5aa7408e4a68 100644
--- a/dom/tests/mochitest/general/test_img_mutations.html
+++ b/dom/tests/mochitest/general/test_img_mutations.html
@@ -69,7 +69,7 @@
       ok(img.currentSrc.endsWith("non_existent_image.404"), "Should have synchronously selected source");
 
       img.removeAttribute("src");
-      is(img.currentSrc, '', "Should have dropped currentSrc");
+      is(img.currentSrc, null, "Should have dropped currentSrc");
 
       // Load another image while previous load is still pending
       img.src = testPNG200;
diff --git a/dom/tests/mochitest/general/test_picture_mutations.html b/dom/tests/mochitest/general/test_picture_mutations.html
index 7dee62456be9..58efbbc3c511 100644
--- a/dom/tests/mochitest/general/test_picture_mutations.html
+++ b/dom/tests/mochitest/general/test_picture_mutations.html
@@ -65,7 +65,7 @@
       info("test 1");
       img.srcset = testPNG100;
       img.src = testPNG50;
-      is(img.currentSrc, '', "Should not have synchronously selected source");
+      is(img.currentSrc, null, "Should not have synchronously selected source");
 
       // No events should have fired synchronously, now we should get just one load (and no 404 error)
       expectEvents(1, 0, nextTest);
diff --git a/dom/webidl/HTMLImageElement.webidl b/dom/webidl/HTMLImageElement.webidl
index fce3c7cdf488..c22c6bf1ad47 100644
--- a/dom/webidl/HTMLImageElement.webidl
+++ b/dom/webidl/HTMLImageElement.webidl
@@ -62,7 +62,7 @@ partial interface HTMLImageElement {
            [SetterThrows, Pref="dom.image.picture.enabled"]
            attribute DOMString sizes;
            [Pref="dom.image.srcset.enabled"]
-  readonly attribute DOMString currentSrc;
+  readonly attribute DOMString? currentSrc;
 };
 
 // Mozilla extensions.