diff --git a/src/hb-ot-layout-gpos-private.hh b/src/hb-ot-layout-gpos-private.hh
index b1523083e..07f5c8ef7 100644
--- a/src/hb-ot-layout-gpos-private.hh
+++ b/src/hb-ot-layout-gpos-private.hh
@@ -317,6 +317,7 @@ struct MarkArray
 		     const AnchorMatrix &anchors, unsigned int class_count,
 		     unsigned int glyph_pos) const
   {
+    APPLY_DEBUG ();
     const MarkRecord &record = markRecord[mark_index];
     unsigned int mark_class = record.klass;
 
@@ -360,6 +361,7 @@ struct SinglePosFormat1
   private:
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     unsigned int index = (this+coverage) (IN_CURGLYPH ());
     if (HB_LIKELY (index == NOT_COVERED))
       return false;
@@ -396,6 +398,7 @@ struct SinglePosFormat2
   private:
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     unsigned int index = (this+coverage) (IN_CURGLYPH ());
     if (HB_LIKELY (index == NOT_COVERED))
       return false;
@@ -437,6 +440,7 @@ struct SinglePos
   private:
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     switch (u.format) {
     case 1: return u.format1->apply (APPLY_ARG);
     case 2: return u.format2->apply (APPLY_ARG);
@@ -503,6 +507,7 @@ struct PairPosFormat1
   private:
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     unsigned int end = MIN (buffer->in_length, buffer->in_pos + context_length);
     if (HB_UNLIKELY (buffer->in_pos + 2 > end))
       return false;
@@ -575,6 +580,7 @@ struct PairPosFormat2
   private:
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     unsigned int end = MIN (buffer->in_length, buffer->in_pos + context_length);
     if (HB_UNLIKELY (buffer->in_pos + 2 > end))
       return false;
@@ -657,6 +663,7 @@ struct PairPos
   private:
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     switch (u.format) {
     case 1: return u.format1->apply (APPLY_ARG);
     case 2: return u.format2->apply (APPLY_ARG);
@@ -709,6 +716,7 @@ struct CursivePosFormat1
   private:
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     /* Now comes the messiest part of the whole OpenType
        specification.  At first glance, cursive connections seem easy
        to understand, but there are pitfalls!  The reason is that
@@ -904,6 +912,7 @@ struct CursivePos
   private:
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     switch (u.format) {
     case 1: return u.format1->apply (APPLY_ARG);
     default:return false;
@@ -941,6 +950,7 @@ struct MarkBasePosFormat1
   private:
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     unsigned int mark_index = (this+markCoverage) (IN_CURGLYPH ());
     if (HB_LIKELY (mark_index == NOT_COVERED))
       return false;
@@ -998,6 +1008,7 @@ struct MarkBasePos
   private:
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     switch (u.format) {
     case 1: return u.format1->apply (APPLY_ARG);
     default:return false;
@@ -1041,6 +1052,7 @@ struct MarkLigPosFormat1
   private:
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     unsigned int mark_index = (this+markCoverage) (IN_CURGLYPH ());
     if (HB_LIKELY (mark_index == NOT_COVERED))
       return false;
@@ -1121,6 +1133,7 @@ struct MarkLigPos
   private:
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     switch (u.format) {
     case 1: return u.format1->apply (APPLY_ARG);
     default:return false;
@@ -1158,6 +1171,7 @@ struct MarkMarkPosFormat1
   private:
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     unsigned int mark1_index = (this+mark1Coverage) (IN_CURGLYPH ());
     if (HB_LIKELY (mark1_index == NOT_COVERED))
       return false;
@@ -1220,6 +1234,7 @@ struct MarkMarkPos
   private:
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     switch (u.format) {
     case 1: return u.format1->apply (APPLY_ARG);
     default:return false;
@@ -1252,7 +1267,10 @@ struct ContextPos : Context
 
   private:
   inline bool apply (APPLY_ARG_DEF) const
-  { return Context::apply (APPLY_ARG, position_lookup); }
+  {
+    APPLY_DEBUG ();
+    return Context::apply (APPLY_ARG, position_lookup);
+  }
 };
 ASSERT_SIZE (ContextPos, 2);
 
@@ -1262,7 +1280,10 @@ struct ChainContextPos : ChainContext
 
   private:
   inline bool apply (APPLY_ARG_DEF) const
-  { return ChainContext::apply (APPLY_ARG, position_lookup); }
+  {
+    APPLY_DEBUG ();
+    return ChainContext::apply (APPLY_ARG, position_lookup);
+  }
 };
 ASSERT_SIZE (ChainContextPos, 2);
 
@@ -1306,6 +1327,7 @@ struct PosLookupSubTable
 
   inline bool apply (APPLY_ARG_DEF, unsigned int lookup_type) const
   {
+    APPLY_DEBUG ();
     switch (lookup_type) {
     case Single:		return u.single->apply (APPLY_ARG);
     case Pair:			return u.pair->apply (APPLY_ARG);
@@ -1392,7 +1414,7 @@ struct PosLookup : Lookup
       return false;
 
     for (unsigned int i = 0; i < get_subtable_count (); i++)
-      if (get_subtable (i).apply (APPLY_ARG, lookup_type))
+      if (get_subtable (i).apply (APPLY_ARG_INIT, lookup_type))
 	return true;
 
     return false;
@@ -1479,6 +1501,7 @@ ASSERT_SIZE (GPOS, 10);
 
 inline bool ExtensionPos::apply (APPLY_ARG_DEF) const
 {
+  APPLY_DEBUG ();
   unsigned int lookup_type = get_type ();
 
   if (HB_UNLIKELY (lookup_type == PosLookupSubTable::Extension))
diff --git a/src/hb-ot-layout-gsub-private.hh b/src/hb-ot-layout-gsub-private.hh
index 4c682fedf..992f4532e 100644
--- a/src/hb-ot-layout-gsub-private.hh
+++ b/src/hb-ot-layout-gsub-private.hh
@@ -38,6 +38,7 @@ struct SingleSubstFormat1
 
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     hb_codepoint_t glyph_id = IN_CURGLYPH ();
     unsigned int index = (this+coverage) (glyph_id);
     if (HB_LIKELY (index == NOT_COVERED))
@@ -76,6 +77,7 @@ struct SingleSubstFormat2
 
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     hb_codepoint_t glyph_id = IN_CURGLYPH ();
     unsigned int index = (this+coverage) (glyph_id);
     if (HB_LIKELY (index == NOT_COVERED))
@@ -118,6 +120,7 @@ struct SingleSubst
 
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     switch (u.format) {
     case 1: return u.format1->apply (APPLY_ARG);
     case 2: return u.format2->apply (APPLY_ARG);
@@ -152,6 +155,7 @@ struct Sequence
   private:
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     if (HB_UNLIKELY (!substitute.len))
       return false;
 
@@ -193,6 +197,7 @@ struct MultipleSubstFormat1
 
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
 
     unsigned int index = (this+coverage) (IN_CURGLYPH ());
     if (HB_LIKELY (index == NOT_COVERED))
@@ -225,6 +230,7 @@ struct MultipleSubst
 
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     switch (u.format) {
     case 1: return u.format1->apply (APPLY_ARG);
     default:return false;
@@ -261,6 +267,7 @@ struct AlternateSubstFormat1
 
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     hb_codepoint_t glyph_id = IN_CURGLYPH ();
 
     unsigned int index = (this+coverage) (glyph_id);
@@ -319,6 +326,7 @@ struct AlternateSubst
 
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     switch (u.format) {
     case 1: return u.format1->apply (APPLY_ARG);
     default:return false;
@@ -350,6 +358,7 @@ struct Ligature
   private:
   inline bool apply (APPLY_ARG_DEF, bool is_mark) const
   {
+    APPLY_DEBUG ();
     unsigned int i, j;
     unsigned int count = component.len;
     unsigned int end = MIN (buffer->in_length, buffer->in_pos + context_length);
@@ -435,6 +444,7 @@ struct LigatureSet
   private:
   inline bool apply (APPLY_ARG_DEF, bool is_mark) const
   {
+    APPLY_DEBUG ();
     unsigned int num_ligs = ligature.len;
     for (unsigned int i = 0; i < num_ligs; i++)
     {
@@ -466,6 +476,7 @@ struct LigatureSubstFormat1
   private:
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     hb_codepoint_t glyph_id = IN_CURGLYPH ();
 
     bool first_is_mark = !!(property & HB_OT_LAYOUT_GLYPH_CLASS_MARK);
@@ -501,6 +512,7 @@ struct LigatureSubst
   private:
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     switch (u.format) {
     case 1: return u.format1->apply (APPLY_ARG);
     default:return false;
@@ -534,7 +546,10 @@ struct ContextSubst : Context
 
   private:
   inline bool apply (APPLY_ARG_DEF) const
-  { return Context::apply (APPLY_ARG, substitute_lookup); }
+  {
+    APPLY_DEBUG ();
+    return Context::apply (APPLY_ARG, substitute_lookup);
+  }
 };
 ASSERT_SIZE (ContextSubst, 2);
 
@@ -544,7 +559,10 @@ struct ChainContextSubst : ChainContext
 
   private:
   inline bool apply (APPLY_ARG_DEF) const
-  { return ChainContext::apply (APPLY_ARG, substitute_lookup); }
+  {
+    APPLY_DEBUG ();
+    return ChainContext::apply (APPLY_ARG, substitute_lookup);
+  }
 };
 ASSERT_SIZE (ChainContextSubst, 2);
 
@@ -571,6 +589,7 @@ struct ReverseChainSingleSubstFormat1
   private:
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     if (HB_UNLIKELY (context_length != NO_CONTEXT))
       return false; /* No chaining to this type */
 
@@ -634,6 +653,7 @@ struct ReverseChainSingleSubst
   private:
   inline bool apply (APPLY_ARG_DEF) const
   {
+    APPLY_DEBUG ();
     switch (u.format) {
     case 1: return u.format1->apply (APPLY_ARG);
     default:return false;
@@ -680,6 +700,7 @@ struct SubstLookupSubTable
 
   inline bool apply (APPLY_ARG_DEF, unsigned int lookup_type) const
   {
+    APPLY_DEBUG ();
     switch (lookup_type) {
     case Single:		return u.single->apply (APPLY_ARG);
     case Multiple:		return u.multiple->apply (APPLY_ARG);
@@ -767,7 +788,7 @@ struct SubstLookup : Lookup
 
     unsigned int count = get_subtable_count ();
     for (unsigned int i = 0; i < count; i++)
-      if (get_subtable (i).apply (APPLY_ARG, lookup_type))
+      if (get_subtable (i).apply (APPLY_ARG_INIT, lookup_type))
 	return true;
 
     return false;
@@ -865,6 +886,7 @@ ASSERT_SIZE (GSUB, 10);
 
 inline bool ExtensionSubst::apply (APPLY_ARG_DEF) const
 {
+  APPLY_DEBUG ();
   unsigned int lookup_type = get_type ();
 
   if (HB_UNLIKELY (lookup_type == SubstLookupSubTable::Extension))
diff --git a/src/hb-ot-layout-gsubgpos-private.hh b/src/hb-ot-layout-gsubgpos-private.hh
index 559ee08f9..0dadbe871 100644
--- a/src/hb-ot-layout-gsubgpos-private.hh
+++ b/src/hb-ot-layout-gsubgpos-private.hh
@@ -31,20 +31,53 @@
 #include "hb-ot-layout-gdef-private.hh"
 
 
+#ifndef HB_DEBUG_APPLY
+#define HB_DEBUG_APPLY HB_DEBUG
+#endif
+
+#if HB_DEBUG_APPLY
+#define APPLY_DEBUG_ARG_DEF	, unsigned int apply_depth
+#define APPLY_DEBUG_ARG		, apply_depth + 1
+#define APPLY_DEBUG_ARG_INIT	, 1
+#define APPLY_DEBUG() \
+	HB_STMT_START { \
+	    if (apply_depth < HB_DEBUG_APPLY) \
+		fprintf (stderr, "APPLY(%p) %-*d-> %s\n", \
+			 (CONST_CHARP (this) == NullPool) ? 0 : this, \
+			 apply_depth, apply_depth, \
+			 __PRETTY_FUNCTION__); \
+	} HB_STMT_END
+#else
+#define APPLY_DEBUG_ARG_DEF
+#define APPLY_DEBUG_ARG
+#define APPLY_DEBUG_ARG_INIT
+#define APPLY_DEBUG() HB_STMT_START {} HB_STMT_END
+#endif
+
 #define APPLY_ARG_DEF \
 	hb_ot_layout_context_t *context, \
 	hb_buffer_t    *buffer, \
 	unsigned int    context_length HB_GNUC_UNUSED, \
 	unsigned int    nesting_level_left HB_GNUC_UNUSED, \
 	unsigned int    lookup_flag, \
-	unsigned int    property HB_GNUC_UNUSED /* propety of first glyph */
+	unsigned int    property HB_GNUC_UNUSED /* propety of first glyph */ \
+	APPLY_DEBUG_ARG_DEF
 #define APPLY_ARG \
 	context, \
 	buffer, \
 	context_length, \
 	nesting_level_left, \
 	lookup_flag, \
-	property
+	property \
+	APPLY_DEBUG_ARG
+#define APPLY_ARG_INIT \
+	context, \
+	buffer, \
+	context_length, \
+	nesting_level_left, \
+	lookup_flag, \
+	property \
+	APPLY_DEBUG_ARG_INIT
 
 
 typedef bool (*match_func_t) (hb_codepoint_t glyph_id, const USHORT &value, char *data);
@@ -257,6 +290,7 @@ struct Rule
   private:
   inline bool apply (APPLY_ARG_DEF, ContextLookupContext &lookup_context) const
   {
+    APPLY_DEBUG ();
     const LookupRecord *lookupRecord = &CONST_CAST (LookupRecord, input, sizeof (input[0]) * (inputCount ? inputCount - 1 : 0));
     return context_lookup (APPLY_ARG,
 			   inputCount, input,
@@ -289,6 +323,7 @@ struct RuleSet
 {
   inline bool apply (APPLY_ARG_DEF, ContextLookupContext &lookup_context) const
   {
+    APPLY_DEBUG ();
     unsigned int num_rules = rule.len;
     for (unsigned int i = 0; i < num_rules; i++)
     {
@@ -318,6 +353,7 @@ struct ContextFormat1
   private:
   inline bool apply (APPLY_ARG_DEF, apply_lookup_func_t apply_func) const
   {
+    APPLY_DEBUG ();
     unsigned int index = (this+coverage) (IN_CURGLYPH ());
     if (HB_LIKELY (index == NOT_COVERED))
       return false;
@@ -354,6 +390,7 @@ struct ContextFormat2
   private:
   inline bool apply (APPLY_ARG_DEF, apply_lookup_func_t apply_func) const
   {
+    APPLY_DEBUG ();
     unsigned int index = (this+coverage) (IN_CURGLYPH ());
     if (HB_LIKELY (index == NOT_COVERED))
       return false;
@@ -398,6 +435,7 @@ struct ContextFormat3
   private:
   inline bool apply (APPLY_ARG_DEF, apply_lookup_func_t apply_func) const
   {
+    APPLY_DEBUG ();
     unsigned int index = (this+coverage[0]) (IN_CURGLYPH ());
     if (HB_LIKELY (index == NOT_COVERED))
       return false;
@@ -441,6 +479,7 @@ struct Context
   protected:
   inline bool apply (APPLY_ARG_DEF, apply_lookup_func_t apply_func) const
   {
+    APPLY_DEBUG ();
     switch (u.format) {
     case 1: return u.format1->apply (APPLY_ARG, apply_func);
     case 2: return u.format2->apply (APPLY_ARG, apply_func);
@@ -522,6 +561,7 @@ struct ChainRule
   private:
   inline bool apply (APPLY_ARG_DEF, ChainContextLookupContext &lookup_context) const
   {
+    APPLY_DEBUG ();
     const HeadlessArrayOf<USHORT> &input = CONST_NEXT (HeadlessArrayOf<USHORT>, backtrack);
     const ArrayOf<USHORT> &lookahead = CONST_NEXT (ArrayOf<USHORT>, input);
     const ArrayOf<LookupRecord> &lookup = CONST_NEXT (ArrayOf<LookupRecord>, lookahead);
@@ -567,6 +607,7 @@ struct ChainRuleSet
 {
   inline bool apply (APPLY_ARG_DEF, ChainContextLookupContext &lookup_context) const
   {
+    APPLY_DEBUG ();
     unsigned int num_rules = rule.len;
     for (unsigned int i = 0; i < num_rules; i++)
     {
@@ -596,6 +637,7 @@ struct ChainContextFormat1
   private:
   inline bool apply (APPLY_ARG_DEF, apply_lookup_func_t apply_func) const
   {
+    APPLY_DEBUG ();
     unsigned int index = (this+coverage) (IN_CURGLYPH ());
     if (HB_LIKELY (index == NOT_COVERED))
       return false;
@@ -631,6 +673,7 @@ struct ChainContextFormat2
   private:
   inline bool apply (APPLY_ARG_DEF, apply_lookup_func_t apply_func) const
   {
+    APPLY_DEBUG ();
     unsigned int index = (this+coverage) (IN_CURGLYPH ());
     if (HB_LIKELY (index == NOT_COVERED))
       return false;
@@ -691,6 +734,7 @@ struct ChainContextFormat3
 
   inline bool apply (APPLY_ARG_DEF, apply_lookup_func_t apply_func) const
   {
+    APPLY_DEBUG ();
     const OffsetArrayOf<Coverage> &input = CONST_NEXT (OffsetArrayOf<Coverage>, backtrack);
 
     unsigned int index = (this+input[0]) (IN_CURGLYPH ());
@@ -748,6 +792,7 @@ struct ChainContext
   protected:
   inline bool apply (APPLY_ARG_DEF, apply_lookup_func_t apply_func) const
   {
+    APPLY_DEBUG ();
     switch (u.format) {
     case 1: return u.format1->apply (APPLY_ARG, apply_func);
     case 2: return u.format2->apply (APPLY_ARG, apply_func);