diff --git a/src/FontLib/AdobeFontMetrics.php b/src/FontLib/AdobeFontMetrics.php
index e902e3e..613117d 100644
--- a/src/FontLib/AdobeFontMetrics.php
+++ b/src/FontLib/AdobeFontMetrics.php
@@ -82,23 +82,24 @@ function write($file, $encoding = null) {
 
     $glyf = $font->getData("glyf");
     $glyphIndexArray = $font->getUnicodeCharMap();
+    $hasGlyphs = $glyf instanceof glyf && is_array($glyphIndexArray);
 
     // capHeight is based on capital H
-    if (\array_key_exists(72, $glyphIndexArray)) {
+    if ($hasGlyphs && \array_key_exists(72, $glyphIndexArray)) {
       $upperH = $glyf[$glyphIndexArray[72]];
       $upperH->parseData();
       $this->addPair("CapHeight", $font->normalizeFUnit($upperH->yMax));
     }
 
     // xHeight is based on lowercase x
-    if (\array_key_exists(120, $glyphIndexArray)) {
+    if ($hasGlyphs && \array_key_exists(120, $glyphIndexArray)) {
       $lowerX = $glyf[$glyphIndexArray[120]];
       $lowerX->parseData();
       $this->addPair("XHeight", $font->normalizeFUnit($lowerX->yMax));
     }
 
     // ascender is based on lowercase d
-    if (\array_key_exists(100, $glyphIndexArray)) {
+    if ($hasGlyphs && \array_key_exists(100, $glyphIndexArray)) {
       $lowerD = $glyf[$glyphIndexArray[100]];
       $lowerD->parseData();
       $this->addPair("Ascender", $font->normalizeFUnit($lowerD->yMax));
@@ -110,11 +111,11 @@ function write($file, $encoding = null) {
     }
 
     // descender is based on lowercase p
-    if (\array_key_exists(112, $glyphIndexArray)) {
+    if ($hasGlyphs && \array_key_exists(112, $glyphIndexArray)) {
       $lowerP = $glyf[$glyphIndexArray[112]];
       $lowerP->parseData();
       $this->addPair("Descender", $font->normalizeFUnit($lowerP->yMin));
-    } elseif (isset($hhea["ascent"])) {
+    } elseif (isset($hhea["descent"])) {
       $this->addPair("Descender", $font->normalizeFUnit($hhea["descent"]));
     }
     else {
diff --git a/src/FontLib/TrueType/File.php b/src/FontLib/TrueType/File.php
index f32d067..b1c7cd8 100644
--- a/src/FontLib/TrueType/File.php
+++ b/src/FontLib/TrueType/File.php
@@ -310,11 +310,11 @@ function setSubset($subset) {
 
     /** @var glyf $glyf */
     $glyf = $this->getTableObject("glyf");
-    $gids = $glyf->getGlyphIDs($gids);
-
-    sort($gids);
-
-    $this->glyph_subset = $gids;
+    if ($glyf) {
+      $gids = $glyf->getGlyphIDs($gids);
+      sort($gids);
+      $this->glyph_subset = $gids;
+    }
     $this->glyph_all    = array_values($glyphIndexArray); // FIXME
   }
 
@@ -443,7 +443,10 @@ protected function readTable($tag) {
    * @return Table
    */
   public function getTableObject($name) {
-    return $this->data[$name];
+    if (\array_key_exists($name, $this->data)) {
+      return $this->data[$name];
+    }
+    return null;
   }
 
   public function setTableObject($name, Table $data) {