diff --git a/src/normalize.cc b/src/normalize.cc
index b538b91..1af3b7d 100644
--- a/src/normalize.cc
+++ b/src/normalize.cc
@@ -52,7 +52,7 @@ bool WriteNormalizedLoca(int index_fmt, int num_glyphs, Font* font) {
   loca_table->buffer.resize(Round4(num_glyphs + 1) * glyph_sz);
   loca_table->length = (num_glyphs + 1) * glyph_sz;
 
-  uint8_t* glyf_dst = &glyf_table->buffer[0];
+  uint8_t* glyf_dst = num_glyphs ? &glyf_table->buffer[0] : NULL;
   uint8_t* loca_dst = &loca_table->buffer[0];
   uint32_t glyf_offset = 0;
   size_t loca_offset = 0;
@@ -78,16 +78,13 @@ bool WriteNormalizedLoca(int index_fmt, int num_glyphs, Font* font) {
     }
     glyf_offset += glyf_dst_size;
   }
-  if (glyf_offset == 0) {
-    return false;
-  }
 
   StoreLoca(index_fmt, glyf_offset, &loca_offset, loca_dst);
 
   glyf_table->buffer.resize(glyf_offset);
-  glyf_table->data = &glyf_table->buffer[0];
+  glyf_table->data = glyf_offset ? &glyf_table->buffer[0] : NULL;
   glyf_table->length = glyf_offset;
-  loca_table->data = &loca_table->buffer[0];
+  loca_table->data = loca_offset ? &loca_table->buffer[0] : NULL;
 
   return true;
 }
diff --git a/src/woff2_enc.cc b/src/woff2_enc.cc
index bc5238f..4e83a67 100644
--- a/src/woff2_enc.cc
+++ b/src/woff2_enc.cc
@@ -34,7 +34,6 @@
 #include "./variable_length.h"
 #include "./woff2_common.h"
 
-
 namespace woff2 {
 
 namespace {
@@ -106,7 +105,8 @@ size_t TableEntrySize(const Table& table) {
 
 size_t ComputeWoff2Length(const FontCollection& font_collection,
                           const std::vector<Table>& tables,
-                          std::map<uint32_t, uint16_t> index_by_offset,
+                          std::map<std::pair<uint32_t, uint32_t>, uint16_t>
+                            index_by_tag_offset,
                           size_t compressed_data_length,
                           size_t extended_metadata_length) {
   size_t size = kWoff2HeaderSize;
@@ -129,7 +129,8 @@ size_t ComputeWoff2Length(const FontCollection& font_collection,
         // no collection entry for xform table
         if (table.tag & 0x80808080) continue;
 
-        uint16_t table_index = index_by_offset[table.offset];
+        std::pair<uint32_t, uint32_t> tag_offset(table.tag, table.offset);
+        uint16_t table_index = index_by_tag_offset[tag_offset];
         size += Size255UShort(table_index);  // 255UInt16 index entry
       }
     }
@@ -321,7 +322,7 @@ bool ConvertTTFToWOFF2(const uint8_t *data, size_t length,
   }
 
   std::vector<Table> tables;
-  std::map<uint32_t, uint16_t> index_by_offset;
+  std::map<std::pair<uint32_t, uint32_t>, uint16_t> index_by_tag_offset;
 
   for (const auto& font : font_collection.fonts) {
 
@@ -331,8 +332,9 @@ bool ConvertTTFToWOFF2(const uint8_t *data, size_t length,
         continue;
       }
 
-      if (index_by_offset.find(src_table.offset) == index_by_offset.end()) {
-        index_by_offset[src_table.offset] = tables.size();
+      std::pair<uint32_t, uint32_t> tag_offset(src_table.tag, src_table.offset);
+      if (index_by_tag_offset.find(tag_offset) == index_by_tag_offset.end()) {
+        index_by_tag_offset[tag_offset] = tables.size();
       } else {
         return false;
       }
@@ -357,7 +359,8 @@ bool ConvertTTFToWOFF2(const uint8_t *data, size_t length,
   }
 
   size_t woff2_length = ComputeWoff2Length(font_collection, tables,
-      index_by_offset, total_compressed_length, compressed_metadata_buf_length);
+      index_by_tag_offset, total_compressed_length,
+      compressed_metadata_buf_length);
   if (woff2_length > *result_length) {
 #ifdef FONT_COMPRESSION_BIN
     fprintf(stderr, "Result allocation was too small (%zd vs %zd bytes).\n",
@@ -430,14 +433,15 @@ bool ConvertTTFToWOFF2(const uint8_t *data, size_t length,
           table.IsReused() ? table.reuse_of->offset : table.offset;
         uint32_t table_length =
           table.IsReused() ? table.reuse_of->length : table.length;
-        if (index_by_offset.find(table_offset) == index_by_offset.end()) {
+        std::pair<uint32_t, uint32_t> tag_offset(table.tag, table_offset);
+        if (index_by_tag_offset.find(tag_offset) == index_by_tag_offset.end()) {
 #ifdef FONT_COMPRESSION_BIN
           fprintf(stderr, "Missing table index for offset 0x%08x\n",
                   table_offset);
 #endif
           return FONT_COMPRESSION_FAILURE();
         }
-        uint16_t index = index_by_offset[table_offset];
+        uint16_t index = index_by_tag_offset[tag_offset];
         Store255UShort(index, &offset, result);
 
       }