diff --git a/layout/generic/nsLineLayout.cpp b/layout/generic/nsLineLayout.cpp
index b5aefd45266c..d0ff43423fc7 100644
--- a/layout/generic/nsLineLayout.cpp
+++ b/layout/generic/nsLineLayout.cpp
@@ -1349,16 +1349,19 @@ void nsLineLayout::PlaceFrame(PerFrameData* pfd, ReflowOutput& aMetrics) {
? lineWM.IsLineInverted() ? 0 : aMetrics.BSize(lineWM)
: aMetrics.BSize(lineWM) / 2;
} else {
- if (pfd->mFrame->StyleDisplay()->mBaselineSource ==
- StyleBaselineSource::Auto) {
+ // For inline reflow participants, baseline may get assigned as the frame is
+ // vertically aligned, which happens after this.
+ const auto baselineSource = pfd->mFrame->StyleDisplay()->mBaselineSource;
+ if (baselineSource == StyleBaselineSource::Auto ||
+ pfd->mFrame->IsFrameOfType(nsIFrame::eLineParticipant)) {
if (aMetrics.BlockStartAscent() == ReflowOutput::ASK_FOR_BASELINE) {
pfd->mAscent = pfd->mFrame->GetLogicalBaseline(lineWM);
} else {
pfd->mAscent = aMetrics.BlockStartAscent();
}
} else {
- const auto sourceGroup = [pfd]() {
- switch (pfd->mFrame->StyleDisplay()->mBaselineSource) {
+ const auto sourceGroup = [baselineSource]() {
+ switch (baselineSource) {
case StyleBaselineSource::First:
return BaselineSharingGroup::First;
case StyleBaselineSource::Last:
diff --git a/testing/web-platform/tests/css/css-inline/baseline-source/baseline-source-inline-box-ref.html b/testing/web-platform/tests/css/css-inline/baseline-source/baseline-source-inline-box-ref.html
new file mode 100644
index 000000000000..ef3077970a29
--- /dev/null
+++ b/testing/web-platform/tests/css/css-inline/baseline-source/baseline-source-inline-box-ref.html
@@ -0,0 +1,11 @@
+
+
+
+
+ a
+
+
diff --git a/testing/web-platform/tests/css/css-inline/baseline-source/baseline-source-inline-box.html b/testing/web-platform/tests/css/css-inline/baseline-source/baseline-source-inline-box.html
new file mode 100644
index 000000000000..cc88067c285c
--- /dev/null
+++ b/testing/web-platform/tests/css/css-inline/baseline-source/baseline-source-inline-box.html
@@ -0,0 +1,18 @@
+
+
+
+
+
+
+
+
+
+ a
+