diff --git a/Lib/fontTools/cffLib.py b/Lib/fontTools/cffLib.py
index b724c62d7..c859265ae 100644
--- a/Lib/fontTools/cffLib.py
+++ b/Lib/fontTools/cffLib.py
@@ -1086,7 +1086,7 @@ class NumberConverter(SimpleConverter):
 
 class ArrayConverter(SimpleConverter):
 	def xmlWrite(self, xmlWriter, name, value, progress):
-		if isinstance(value[0], list):
+		if value and isinstance(value[0], list):
 			xmlWriter.begintag(name)
 			xmlWriter.newline()
 			xmlWriter.indent()
@@ -1907,6 +1907,8 @@ class DictCompiler(object):
 			data.append(self.arg_number(num))
 		return bytesjoin(data)
 	def arg_delta(self, value):
+		if not value:
+			return b""
 		val0 = value[0]
 		if isinstance(val0, list):
 			data = self.arg_delta_blend(value)
diff --git a/Lib/fontTools/misc/psCharStrings.py b/Lib/fontTools/misc/psCharStrings.py
index 3976cbe8b..fc9ff5da1 100644
--- a/Lib/fontTools/misc/psCharStrings.py
+++ b/Lib/fontTools/misc/psCharStrings.py
@@ -1319,7 +1319,8 @@ class DictDecompiler(ByteCodeBase):
 	def arg_delta(self, name):
 		valueList = self.popall()
 		out = []
-		if isinstance(valueList[0], list): # arg_blendList() has already converted these to absolute values.
+		if valueList and isinstance(valueList[0], list):
+			# arg_blendList() has already converted these to absolute values.
 			out = valueList
 		else:
 			current = 0