diff --git a/layout/base/nsCSSRendering.cpp b/layout/base/nsCSSRendering.cpp
index fb374dfbf6b..05d0782fb19 100644
--- a/layout/base/nsCSSRendering.cpp
+++ b/layout/base/nsCSSRendering.cpp
@@ -3894,7 +3894,7 @@ nsCSSRendering::PaintRoundedBackground(nsPresContext* aPresContext,
aRenderingContext.GetNativeGraphicData(nsIRenderingContext::NATIVE_THEBES_CONTEXT);
// needed for our border thickness
- nscoord appUnitsPerPixel = nsPresContext::AppUnitsPerCSSPixel();
+ nscoord appUnitsPerPixel = aPresContext->AppUnitsPerDevPixel();
nscolor color = aColor.mBackgroundColor;
if (!aCanPaintNonWhite) {
diff --git a/layout/reftests/bugs/384576-1-ref.html b/layout/reftests/bugs/384576-1-ref.html
new file mode 100644
index 00000000000..58a84349004
--- /dev/null
+++ b/layout/reftests/bugs/384576-1-ref.html
@@ -0,0 +1,15 @@
+
+
+
+
+
+
diff --git a/layout/reftests/bugs/384576-1.html b/layout/reftests/bugs/384576-1.html
new file mode 100644
index 00000000000..d78b6c81706
--- /dev/null
+++ b/layout/reftests/bugs/384576-1.html
@@ -0,0 +1,16 @@
+
+
+
+
+
+
diff --git a/layout/reftests/bugs/reftest.list b/layout/reftests/bugs/reftest.list
index 8d6f5a6835b..a3335b08d55 100644
--- a/layout/reftests/bugs/reftest.list
+++ b/layout/reftests/bugs/reftest.list
@@ -275,3 +275,4 @@ random-if(MOZ_WIDGET_TOOLKIT=="cocoa") == 379316-2.html 379316-2-ref.html # bug
== 381507-1.html 381507-1-ref.html
== 382600-1.html 382600-1-ref.html
== 383551-1.html 383551-1-ref.html
+== 384576-1.html 384576-1-ref.html