diff --git a/src/hb-ot-shape-complex-arabic.cc b/src/hb-ot-shape-complex-arabic.cc
index 4da8990558ac23fed12ae08cd57ec50296a5d648..56ec5cd65cfb38b0d86e8c33300d0b8119a1680a 100644
--- a/src/hb-ot-shape-complex-arabic.cc
+++ b/src/hb-ot-shape-complex-arabic.cc
@@ -618,6 +618,7 @@ const hb_ot_complex_shaper_t _hb_ot_complex_shaper_arabic =
   NULL, /* decompose */
   NULL, /* compose */
   setup_masks_arabic,
+  NULL, /* disable_otl */
   HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_LATE,
   true, /* fallback_position */
 };
diff --git a/src/hb-ot-shape-complex-default.cc b/src/hb-ot-shape-complex-default.cc
index be60e56feb8beaf5015590928556fbdaf716ff39..42830ab6185712ba04dead6b1117c1a3d64398dc 100644
--- a/src/hb-ot-shape-complex-default.cc
+++ b/src/hb-ot-shape-complex-default.cc
@@ -40,6 +40,7 @@ const hb_ot_complex_shaper_t _hb_ot_complex_shaper_default =
   NULL, /* decompose */
   NULL, /* compose */
   NULL, /* setup_masks */
+  NULL, /* disable_otl */
   HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_LATE,
   true, /* fallback_position */
 };
diff --git a/src/hb-ot-shape-complex-hangul.cc b/src/hb-ot-shape-complex-hangul.cc
index 5f4d98b70c8136b21b8de730b6d2df10e520d797..eb95a28c09c7d9ea1a8411b4fc9f8ece587a91e4 100644
--- a/src/hb-ot-shape-complex-hangul.cc
+++ b/src/hb-ot-shape-complex-hangul.cc
@@ -419,6 +419,7 @@ const hb_ot_complex_shaper_t _hb_ot_complex_shaper_hangul =
   NULL, /* decompose */
   NULL, /* compose */
   setup_masks_hangul,
+  NULL, /* disable_otl */
   HB_OT_SHAPE_ZERO_WIDTH_MARKS_NONE,
   false, /* fallback_position */
 };
diff --git a/src/hb-ot-shape-complex-hebrew.cc b/src/hb-ot-shape-complex-hebrew.cc
index 32159002e9344e22ef3c283e857e56e2f90cf69d..96f24946165f362dd560812b4496baa3fd734f54 100644
--- a/src/hb-ot-shape-complex-hebrew.cc
+++ b/src/hb-ot-shape-complex-hebrew.cc
@@ -154,6 +154,18 @@ compose_hebrew (const hb_ot_shape_normalize_context_t *c,
   return found;
 }
 
+static bool
+disable_otl_hebrew (const hb_ot_shape_plan_t *plan)
+{
+  /* For Hebrew shaper, use fallback if GPOS does not have 'hebr'
+   * script.  This matches Uniscribe better, and makes fonts like
+   * Arial that have GSUB/GPOS/GDEF but no data for Hebrew work.
+   * See:
+   * https://github.com/behdad/harfbuzz/issues/347#issuecomment-267838368
+   */
+  return plan->map.chosen_script[1] != HB_TAG ('h','e','b','r');
+}
+
 
 const hb_ot_complex_shaper_t _hb_ot_complex_shaper_hebrew =
 {
@@ -168,6 +180,7 @@ const hb_ot_complex_shaper_t _hb_ot_complex_shaper_hebrew =
   NULL, /* decompose */
   compose_hebrew,
   NULL, /* setup_masks */
+  disable_otl_hebrew,
   HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_LATE,
   true, /* fallback_position */
 };
diff --git a/src/hb-ot-shape-complex-indic.cc b/src/hb-ot-shape-complex-indic.cc
index 94556f65470e45eed0a9acbbd5154392ef847583..ec6e82c4f94a237752a0272116e6f321e8d322ad 100644
--- a/src/hb-ot-shape-complex-indic.cc
+++ b/src/hb-ot-shape-complex-indic.cc
@@ -1819,6 +1819,7 @@ const hb_ot_complex_shaper_t _hb_ot_complex_shaper_indic =
   decompose_indic,
   compose_indic,
   setup_masks_indic,
+  NULL, /* disable_otl */
   HB_OT_SHAPE_ZERO_WIDTH_MARKS_NONE,
   false, /* fallback_position */
 };
diff --git a/src/hb-ot-shape-complex-myanmar.cc b/src/hb-ot-shape-complex-myanmar.cc
index 577d790c783e86b14fb233915cd91460aa4c19ac..bb68622e2a7d13589131cf3a5753d780933752ab 100644
--- a/src/hb-ot-shape-complex-myanmar.cc
+++ b/src/hb-ot-shape-complex-myanmar.cc
@@ -521,6 +521,7 @@ const hb_ot_complex_shaper_t _hb_ot_complex_shaper_myanmar_old =
   NULL, /* decompose */
   NULL, /* compose */
   NULL, /* setup_masks */
+  NULL, /* disable_otl */
   HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_LATE,
   true, /* fallback_position */
 };
@@ -538,6 +539,7 @@ const hb_ot_complex_shaper_t _hb_ot_complex_shaper_myanmar =
   NULL, /* decompose */
   NULL, /* compose */
   setup_masks_myanmar,
+  NULL, /* disable_otl */
   HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_EARLY,
   false, /* fallback_position */
 };
diff --git a/src/hb-ot-shape-complex-private.hh b/src/hb-ot-shape-complex-private.hh
index fb0c70406178e26601a733df59bdca182bac82a2..39572dfe0079f593789c7897dafaf0595f654d9b 100644
--- a/src/hb-ot-shape-complex-private.hh
+++ b/src/hb-ot-shape-complex-private.hh
@@ -146,6 +146,14 @@ struct hb_ot_complex_shaper_t
 		       hb_buffer_t              *buffer,
 		       hb_font_t                *font);
 
+  /* disable_otl()
+   * Called during shape().
+   * If set and returns true, GDEF/GSUB/GPOS of the font are ignored
+   * and fallback operations used.
+   * May be NULL.
+   */
+  bool (*disable_otl) (const hb_ot_shape_plan_t *plan);
+
   hb_ot_shape_zero_width_marks_type_t zero_width_marks;
 
   bool fallback_position;
diff --git a/src/hb-ot-shape-complex-thai.cc b/src/hb-ot-shape-complex-thai.cc
index 4322b0d1d636d6aef2f3d39369d6255d54a72361..e6f80f59e7f81248069a7c2a914a6d67a26145ba 100644
--- a/src/hb-ot-shape-complex-thai.cc
+++ b/src/hb-ot-shape-complex-thai.cc
@@ -376,6 +376,7 @@ const hb_ot_complex_shaper_t _hb_ot_complex_shaper_thai =
   NULL, /* decompose */
   NULL, /* compose */
   NULL, /* setup_masks */
+  NULL, /* disable_otl */
   HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_LATE,
   false,/* fallback_position */
 };
diff --git a/src/hb-ot-shape-complex-tibetan.cc b/src/hb-ot-shape-complex-tibetan.cc
index a77b531daa5ac02f91fbf334ed406605ef46befe..aadf59f5addd6a11093b199df0debd313c7eb27f 100644
--- a/src/hb-ot-shape-complex-tibetan.cc
+++ b/src/hb-ot-shape-complex-tibetan.cc
@@ -57,6 +57,7 @@ const hb_ot_complex_shaper_t _hb_ot_complex_shaper_tibetan =
   NULL, /* decompose */
   NULL, /* compose */
   NULL, /* setup_masks */
+  NULL, /* disable_otl */
   HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_LATE,
   true, /* fallback_position */
 };
diff --git a/src/hb-ot-shape-complex-use.cc b/src/hb-ot-shape-complex-use.cc
index 045ead52f680dbe59d6e4a7e98f0fa7768c18700..13c7ab3bca7077a586c972771c7bab041b818d22 100644
--- a/src/hb-ot-shape-complex-use.cc
+++ b/src/hb-ot-shape-complex-use.cc
@@ -585,6 +585,7 @@ const hb_ot_complex_shaper_t _hb_ot_complex_shaper_use =
   NULL, /* decompose */
   compose_use,
   setup_masks_use,
+  NULL, /* disable_otl */
   HB_OT_SHAPE_ZERO_WIDTH_MARKS_BY_GDEF_EARLY,
   false, /* fallback_position */
 };
diff --git a/src/hb-ot-shape.cc b/src/hb-ot-shape.cc
index cf916cc82037bd30d3900f172b4d8e6b216e3bdc..ddd6662e8454be782dd282087ac59fd95204d9e0 100644
--- a/src/hb-ot-shape.cc
+++ b/src/hb-ot-shape.cc
@@ -218,6 +218,8 @@ struct hb_ot_shape_context_t
   unsigned int        num_user_features;
 
   /* Transient stuff */
+  bool fallback_positioning;
+  bool fallback_glyph_classes;
   hb_direction_t target_direction;
 };
 
@@ -571,7 +573,7 @@ hb_ot_substitute_default (hb_ot_shape_context_t *c)
   hb_ot_shape_setup_masks (c);
 
   /* This is unfortunate to go here, but necessary... */
-  if (!hb_ot_layout_has_positioning (c->face))
+  if (c->fallback_positioning)
     _hb_ot_shape_fallback_position_recategorize_marks (c->plan, c->font, buffer);
 
   hb_ot_map_glyphs_fast (buffer);
@@ -667,14 +669,12 @@ hb_ot_position_default (hb_ot_shape_context_t *c)
     _hb_ot_shape_fallback_spaces (c->plan, c->font, c->buffer);
 }
 
-static inline bool
+static inline void
 hb_ot_position_complex (hb_ot_shape_context_t *c)
 {
   hb_ot_layout_position_start (c->font, c->buffer);
 
-  bool ret = false;
   unsigned int count = c->buffer->len;
-  bool has_positioning = (bool) hb_ot_layout_has_positioning (c->face);
 
   /* If the font has no GPOS, AND, no fallback positioning will
    * happen, AND, direction is forward, then when zeroing mark
@@ -685,8 +685,9 @@ hb_ot_position_complex (hb_ot_shape_context_t *c)
    * If fallback positinoing happens or GPOS is present, we don't
    * care.
    */
-  bool adjust_offsets_when_zeroing = !(has_positioning || c->plan->shaper->fallback_position ||
-                                       HB_DIRECTION_IS_BACKWARD (c->buffer->props.direction));
+  bool adjust_offsets_when_zeroing = c->fallback_positioning &&
+				     !c->plan->shaper->fallback_position &&
+				     HB_DIRECTION_IS_FORWARD (c->buffer->props.direction);
 
   switch (c->plan->shaper->zero_width_marks)
   {
@@ -700,7 +701,7 @@ hb_ot_position_complex (hb_ot_shape_context_t *c)
       break;
   }
 
-  if (has_positioning)
+  if (likely (!c->fallback_positioning))
   {
     hb_glyph_info_t *info = c->buffer->info;
     hb_glyph_position_t *pos = c->buffer->pos;
@@ -723,7 +724,6 @@ hb_ot_position_complex (hb_ot_shape_context_t *c)
 					  &pos[i].x_offset,
 					  &pos[i].y_offset);
 
-    ret = true;
   }
 
   switch (c->plan->shaper->zero_width_marks)
@@ -742,8 +742,6 @@ hb_ot_position_complex (hb_ot_shape_context_t *c)
   hb_ot_layout_position_finish_advances (c->font, c->buffer);
   hb_ot_zero_width_default_ignorables (c);
   hb_ot_layout_position_finish_offsets (c->font, c->buffer);
-
-  return ret;
 }
 
 static inline void
@@ -753,9 +751,9 @@ hb_ot_position (hb_ot_shape_context_t *c)
 
   hb_ot_position_default (c);
 
-  hb_bool_t fallback = !hb_ot_position_complex (c);
+  hb_ot_position_complex (c);
 
-  if (fallback && c->plan->shaper->fallback_position)
+  if (c->fallback_positioning && c->plan->shaper->fallback_position)
     _hb_ot_shape_fallback_position (c->plan, c->font, c->buffer);
 
   if (HB_DIRECTION_IS_BACKWARD (c->buffer->props.direction))
@@ -763,7 +761,7 @@ hb_ot_position (hb_ot_shape_context_t *c)
 
   /* Visual fallback goes here. */
 
-  if (fallback)
+  if (c->fallback_positioning)
     _hb_ot_shape_fallback_kern (c->plan, c->font, c->buffer);
 
   _hb_buffer_deallocate_gsubgpos_vars (c->buffer);
@@ -783,6 +781,11 @@ hb_ot_shape_internal (hb_ot_shape_context_t *c)
 			      (unsigned) HB_BUFFER_MAX_LEN_MIN);
   }
 
+  bool disable_otl = c->plan->shaper->disable_otl && c->plan->shaper->disable_otl (c->plan);
+  //c->fallback_substitute     = disable_otl || !hb_ot_layout_has_substitution (c->face);
+  c->fallback_positioning    = disable_otl || !hb_ot_layout_has_positioning (c->face);
+  c->fallback_glyph_classes  = disable_otl || !hb_ot_layout_has_glyph_classes (c->face);
+
   /* Save the original direction, we use it later. */
   c->target_direction = c->buffer->props.direction;