diff --git a/src/hb-ot-tag.cc b/src/hb-ot-tag.cc
index dcae8f199..ac60e960a 100644
--- a/src/hb-ot-tag.cc
+++ b/src/hb-ot-tag.cc
@@ -651,6 +651,14 @@ hb_ot_tag_from_language (hb_language_t language)
     return HB_TAG('Z','H','S',' ');
   }
 
+  s = strchr (lang_str, '-');
+  if (!s)
+    s = lang_str + strlen (lang_str);
+  if (s - lang_str == 3) {
+    /* Assume it's ISO-639-3 and upper-case and use it. */
+    return hb_tag_from_string (lang_str, s - lang_str) & ~0x20202000;
+  }
+
   return HB_OT_TAG_DEFAULT_LANGUAGE;
 }
 
diff --git a/test/test-ot-tag.c b/test/test-ot-tag.c
index a00799d06..81b667840 100644
--- a/test/test-ot-tag.c
+++ b/test/test-ot-tag.c
@@ -213,12 +213,17 @@ test_ot_tag_language (void)
 
   test_tag_from_language ("dflt", "asdf-asdf-wer-x-hbot-zxc");
 
+  test_tag_from_language ("dflt", "xy");
+  test_tag_from_language ("XYZ", "xyz"); /* Unknown ISO 639-3 */
+  test_tag_from_language ("XYZ", "xyz-qw"); /* Unknown ISO 639-3 */
+
   /* Test that x-hbot overrides the base language */
   test_tag_from_language ("ABC", "fa-x-hbotabc-zxc");
   test_tag_from_language ("ABC", "fa-ir-x-hbotabc-zxc");
   test_tag_from_language ("ABC", "zh-x-hbotabc-zxc");
   test_tag_from_language ("ABC", "zh-cn-x-hbotabc-zxc");
   test_tag_from_language ("ABC", "zh-xy-x-hbotabc-zxc");
+  test_tag_from_language ("ABC", "xyz-xy-x-hbotabc-zxc");
 }
 
 int