diff --git a/icu4c/source/layout/ExtensionSubtables.cpp b/icu4c/source/layout/ExtensionSubtables.cpp
new file mode 100644
index 0000000000..3453743e40
--- /dev/null
+++ b/icu4c/source/layout/ExtensionSubtables.cpp
@@ -0,0 +1,35 @@
+/*
+ * %W% %E%
+ *
+ * (C) Copyright IBM Corp. 2002 - All Rights Reserved
+ *
+ */
+
+#include "LETypes.h"
+#include "OpenTypeTables.h"
+#include "GlyphSubstitutionTables.h"
+#include "LookupProcessor.h"
+#include "ExtensionSubtables.h"
+#include "GlyphIterator.h"
+#include "LESwaps.h"
+
+U_NAMESPACE_BEGIN
+
+
+// FIXME: should look at the format too... maybe have a sub-class for it?
+le_uint32 ExtensionSubtable::process(const LookupProcessor *lookupProcessor, le_uint16 lookupType,
+                                      GlyphIterator *glyphIterator, const LEFontInstance *fontInstance) const
+{
+    le_uint16 elt = SWAPW(extensionLookupType);
+
+    if (elt != lookupType) {
+        le_uint32 extOffset = SWAPL(extensionOffset);
+        LookupSubtable *subtable = (LookupSubtable *) ((char *) this + extOffset);
+
+        return lookupProcessor->applySubtable(subtable, elt, glyphIterator, fontInstance);
+    }
+
+    return 0;
+}
+
+U_NAMESPACE_END
diff --git a/icu4c/source/layout/ExtensionSubtables.h b/icu4c/source/layout/ExtensionSubtables.h
new file mode 100644
index 0000000000..f33d346ba3
--- /dev/null
+++ b/icu4c/source/layout/ExtensionSubtables.h
@@ -0,0 +1,30 @@
+/*
+ * %W% %E%
+ *
+ * (C) Copyright IBM Corp. 2002 - All Rights Reserved
+ *
+ */
+
+#ifndef __EXTENSIONSUBTABLES_H
+#define __EXTENSIONSUBTABLES_H
+
+#include "LETypes.h"
+#include "OpenTypeTables.h"
+#include "GlyphSubstitutionTables.h"
+#include "LookupProcessor.h"
+#include "GlyphIterator.h"
+
+U_NAMESPACE_BEGIN
+
+struct ExtensionSubtable //: GlyphSubstitutionSubtable
+{
+    le_uint16 substFormat;
+    le_uint16 extensionLookupType;
+    le_uint32 extensionOffset;
+
+    le_uint32 process(const LookupProcessor *lookupProcessor, le_uint16 lookupType,
+                      GlyphIterator *glyphIterator, const LEFontInstance *fontInstance) const;
+};
+
+U_NAMESPACE_END
+#endif
diff --git a/icu4c/source/layout/GlyphPositioningTables.h b/icu4c/source/layout/GlyphPositioningTables.h
index 67cd15e188..daa891199c 100644
--- a/icu4c/source/layout/GlyphPositioningTables.h
+++ b/icu4c/source/layout/GlyphPositioningTables.h
@@ -40,7 +40,8 @@ enum GlyphPositioningSubtableTypes
     gpstMarkToLigature  = 5,
     gpstMarkToMark      = 6,
     gpstContext         = 7,
-    gpstChainedContext  = 8
+    gpstChainedContext  = 8,
+    gpstExtension       = 9
 };
 
 typedef LookupSubtable GlyphPositioningSubtable;
diff --git a/icu4c/source/layout/GlyphPosnLookupProc.cpp b/icu4c/source/layout/GlyphPosnLookupProc.cpp
index 71c69aa70d..50855ebe27 100644
--- a/icu4c/source/layout/GlyphPosnLookupProc.cpp
+++ b/icu4c/source/layout/GlyphPosnLookupProc.cpp
@@ -21,6 +21,7 @@
 #include "MarkToMarkPosnSubtables.h"
 //#include "ContextualPositioningSubtables.h"
 #include "ContextualSubstSubtables.h"
+#include "ExtensionSubtables.h"
 #include "LookupProcessor.h"
 #include "GlyphPosnLookupProc.h"
 #include "LESwaps.h"
@@ -124,6 +125,14 @@ le_uint32 GlyphPositioningLookupProcessor::applySubtable(const LookupSubtable *l
         break;
     }
 
+    case gpstExtension:
+    {
+        const ExtensionSubtable *subtable = (const ExtensionSubtable *) lookupSubtable;
+
+        delta = subtable->process(this, lookupType, glyphIterator, fontInstance);
+        break;
+    }
+
     default:
         break;
     }
diff --git a/icu4c/source/layout/GlyphSubstLookupProc.cpp b/icu4c/source/layout/GlyphSubstLookupProc.cpp
index d7574502a6..1d0f0086a9 100644
--- a/icu4c/source/layout/GlyphSubstLookupProc.cpp
+++ b/icu4c/source/layout/GlyphSubstLookupProc.cpp
@@ -19,6 +19,7 @@
 #include "AlternateSubstSubtables.h"
 #include "LigatureSubstSubtables.h"
 #include "ContextualSubstSubtables.h"
+#include "ExtensionSubtables.h"
 #include "LookupProcessor.h"
 #include "GlyphSubstLookupProc.h"
 #include "LESwaps.h"
@@ -100,6 +101,14 @@ le_uint32 GlyphSubstitutionLookupProcessor::applySubtable(const LookupSubtable *
         break;
     }
 
+    case gsstExtension:
+    {
+        const ExtensionSubtable *subtable = (const ExtensionSubtable *) lookupSubtable;
+
+        delta = subtable->process(this, lookupType, glyphIterator, fontInstance);
+        break;
+    }
+
     default:
         break;
     }
diff --git a/icu4c/source/layout/GlyphSubstitutionTables.h b/icu4c/source/layout/GlyphSubstitutionTables.h
index 3e1a08da1f..f33b568741 100644
--- a/icu4c/source/layout/GlyphSubstitutionTables.h
+++ b/icu4c/source/layout/GlyphSubstitutionTables.h
@@ -39,7 +39,9 @@ enum GlyphSubstitutionSubtableTypes
     gsstAlternate       = 3,
     gsstLigature        = 4,
     gsstContext         = 5,
-    gsstChainingContext = 6
+    gsstChainingContext = 6,
+    gsstExtension       = 7,
+    gsstReverseChaining = 8
 };
 
 typedef LookupSubtable GlyphSubstitutionSubtable;
diff --git a/icu4c/source/layout/layout.dsp b/icu4c/source/layout/layout.dsp
index 3301c5544c..198baff453 100644
--- a/icu4c/source/layout/layout.dsp
+++ b/icu4c/source/layout/layout.dsp
@@ -194,6 +194,10 @@ SOURCE=.\DeviceTables.cpp
 # End Source File
 # Begin Source File
 
+SOURCE=.\ExtensionSubtables.cpp
+# End Source File
+# Begin Source File
+
 SOURCE=.\Features.cpp
 # End Source File
 # Begin Source File
@@ -446,6 +450,10 @@ SOURCE=.\DeviceTables.h
 # End Source File
 # Begin Source File
 
+SOURCE=.\ExtensionSubtables.h
+# End Source File
+# Begin Source File
+
 SOURCE=.\Features.h
 # End Source File
 # Begin Source File