diff --git a/src/hb-ot-shape.cc b/src/hb-ot-shape.cc
index ddd6662e8454be782dd282087ac59fd95204d9e0..6b38739c91b6942c3cd8032ce9701528ad031074 100644
--- a/src/hb-ot-shape.cc
+++ b/src/hb-ot-shape.cc
@@ -362,6 +362,18 @@ hb_ot_shape_setup_masks_fraction (hb_ot_shape_context_t *c)
 
   hb_buffer_t *buffer = c->buffer;
 
+  hb_mask_t pre_mask, post_mask;
+  if (HB_DIRECTION_IS_FORWARD (buffer->props.direction))
+  {
+    pre_mask = c->plan->numr_mask | c->plan->frac_mask;
+    post_mask = c->plan->frac_mask | c->plan->dnom_mask;
+  }
+  else
+  {
+    pre_mask = c->plan->frac_mask | c->plan->dnom_mask;
+    post_mask = c->plan->numr_mask | c->plan->frac_mask;
+  }
+
   /* TODO look in pre/post context text also. */
   unsigned int count = buffer->len;
   hb_glyph_info_t *info = buffer->info;
@@ -380,10 +392,10 @@ hb_ot_shape_setup_masks_fraction (hb_ot_shape_context_t *c)
         end++;
 
       for (unsigned int j = start; j < i; j++)
-        info[j].mask |= c->plan->numr_mask | c->plan->frac_mask;
+        info[j].mask |= pre_mask;
       info[i].mask |= c->plan->frac_mask;
       for (unsigned int j = i + 1; j < end; j++)
-        info[j].mask |= c->plan->frac_mask | c->plan->dnom_mask;
+        info[j].mask |= post_mask;
 
       i = end - 1;
     }
diff --git a/test/shaping/Makefile.am b/test/shaping/Makefile.am
index f2bb95bdd22215c3a747f727a85ae7a77a6b7b22..ea0b28a7ebab6438aab74d10e1346b7c39dda0e4 100644
--- a/test/shaping/Makefile.am
+++ b/test/shaping/Makefile.am
@@ -43,6 +43,7 @@ CLEANFILES += \
 TESTS = \
 	tests/arabic-fallback-shaping.tests \
 	tests/arabic-feature-order.tests \
+	tests/automatic-fractions.tests \
 	tests/cluster.tests \
 	tests/color-fonts.tests \
 	tests/context-matching.tests \
diff --git a/test/shaping/fonts/sha1sum/15dfc433a135a658b9f4b1a861b5cdd9658ccbb9.ttf b/test/shaping/fonts/sha1sum/15dfc433a135a658b9f4b1a861b5cdd9658ccbb9.ttf
new file mode 100644
index 0000000000000000000000000000000000000000..4b80f80443b099f82927f924a4434818d76394ad
Binary files /dev/null and b/test/shaping/fonts/sha1sum/15dfc433a135a658b9f4b1a861b5cdd9658ccbb9.ttf differ
diff --git a/test/shaping/tests/automatic-fractions.tests b/test/shaping/tests/automatic-fractions.tests
new file mode 100644
index 0000000000000000000000000000000000000000..f9510e26c938a01021d8dbf20e0b61ce21c2dad0
--- /dev/null
+++ b/test/shaping/tests/automatic-fractions.tests
@@ -0,0 +1,3 @@
+fonts/sha1sum/15dfc433a135a658b9f4b1a861b5cdd9658ccbb9.ttf::U+0031,U+0032,U+0033,U+2044,U+0034,U+0035,U+0036:[one.numr=0+600|two.numr=1+600|three.numr=2+600|fraction=3+252|four.small=4+600|five.small=5+600|six.small=6+600]
+fonts/sha1sum/15dfc433a135a658b9f4b1a861b5cdd9658ccbb9.ttf:--direction=l --script=arab:U+0031,U+0032,U+0033,U+2044,U+0034,U+0035,U+0036:[one.numr=0+600|two.numr=1+600|three.numr=2+600|fraction=3+252|four.small=4+600|five.small=5+600|six.small=6+600]
+fonts/sha1sum/15dfc433a135a658b9f4b1a861b5cdd9658ccbb9.ttf:--direction=l:U+0661,U+0662,U+0663,U+2044,U+0664,U+0665,U+0666:[uni0661.numr=0+600|uni0662.numr=1+600|uni0663.numr=2+600|fraction=3+252|uni0664.small=4+600|uni0665.small=5+600|uni0666.small=6+600]