diff --git a/layout/reftests/text-transform/greek-uppercase-1-ref.html b/layout/reftests/text-transform/greek-uppercase-1-ref.html
index 2dbfe43afa0..ec38eb46982 100644
--- a/layout/reftests/text-transform/greek-uppercase-1-ref.html
+++ b/layout/reftests/text-transform/greek-uppercase-1-ref.html
@@ -5,7 +5,7 @@
 <meta http-equiv="content-type" content="text/html; charset=utf-8">
 <style type="text/css">
 div {
-  font: 150% serif;
+  font: 150% "Droid Serif", serif; /* explicitly prefer Droid over Charis on Android */
   margin: 1em;
 }
 </style>
diff --git a/layout/reftests/text-transform/greek-uppercase-1.html b/layout/reftests/text-transform/greek-uppercase-1.html
index e925472ab5f..af620e9675f 100644
--- a/layout/reftests/text-transform/greek-uppercase-1.html
+++ b/layout/reftests/text-transform/greek-uppercase-1.html
@@ -4,8 +4,12 @@
 <title>Test for uppercasing of Greek (NFC)</title>
 <meta http-equiv="content-type" content="text/html; charset=utf-8">
 <style type="text/css">
+/* Note that this test depends on finding the same "serif" font for the
+   English- and Greek-tagged elements; on most platforms, our default prefs
+   provide that, but on Android they currently differ, hence the explicit
+   Droid Serif setting below. */
 div {
-  font: 150% serif;
+  font: 150% "Droid Serif", serif; /* explicitly prefer Droid over Charis on Android */
   text-transform: uppercase;
   margin: 1em;
 }