diff --git a/src/hb-ot-shape-complex-arabic.cc b/src/hb-ot-shape-complex-arabic.cc
index 4da8990..56ec5cd 100644
--- a/src/hb-ot-shape-complex-arabic.cc
+++ b/src/hb-ot-shape-complex-arabic.cc
@@ -618,6 +618,7 @@
   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 be60e56..42830ab 100644
--- a/src/hb-ot-shape-complex-default.cc
+++ b/src/hb-ot-shape-complex-default.cc
@@ -40,6 +40,7 @@
   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 5f4d98b..eb95a28 100644
--- a/src/hb-ot-shape-complex-hangul.cc
+++ b/src/hb-ot-shape-complex-hangul.cc
@@ -419,6 +419,7 @@
   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 3215900..96f2494 100644
--- a/src/hb-ot-shape-complex-hebrew.cc
+++ b/src/hb-ot-shape-complex-hebrew.cc
@@ -154,6 +154,18 @@
   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 @@
   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 94556f6..ec6e82c 100644
--- a/src/hb-ot-shape-complex-indic.cc
+++ b/src/hb-ot-shape-complex-indic.cc
@@ -1819,6 +1819,7 @@
   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 577d790..bb68622 100644
--- a/src/hb-ot-shape-complex-myanmar.cc
+++ b/src/hb-ot-shape-complex-myanmar.cc
@@ -521,6 +521,7 @@
   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 @@
   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 fb0c704..39572df 100644
--- a/src/hb-ot-shape-complex-private.hh
+++ b/src/hb-ot-shape-complex-private.hh
@@ -146,6 +146,14 @@
 		       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 4322b0d..e6f80f5 100644
--- a/src/hb-ot-shape-complex-thai.cc
+++ b/src/hb-ot-shape-complex-thai.cc
@@ -376,6 +376,7 @@
   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 a77b531..aadf59f 100644
--- a/src/hb-ot-shape-complex-tibetan.cc
+++ b/src/hb-ot-shape-complex-tibetan.cc
@@ -57,6 +57,7 @@
   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 045ead5..13c7ab3 100644
--- a/src/hb-ot-shape-complex-use.cc
+++ b/src/hb-ot-shape-complex-use.cc
@@ -585,6 +585,7 @@
   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 cf916cc..ddd6662 100644
--- a/src/hb-ot-shape.cc
+++ b/src/hb-ot-shape.cc
@@ -218,6 +218,8 @@
   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_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_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 @@
    * 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 @@
       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 @@
 					  &pos[i].x_offset,
 					  &pos[i].y_offset);
 
-    ret = true;
   }
 
   switch (c->plan->shaper->zero_width_marks)
@@ -742,8 +742,6 @@
   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_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 @@
 
   /* 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 @@
 			      (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;