diff --git a/Lib/fontTools/cffLib/__init__.py b/Lib/fontTools/cffLib/__init__.py
index 226216f7c..9b1f04a16 100644
--- a/Lib/fontTools/cffLib/__init__.py
+++ b/Lib/fontTools/cffLib/__init__.py
@@ -4,7 +4,7 @@ from __future__ import print_function, division, absolute_import
 from fontTools.misc.py23 import *
 from fontTools.misc import sstruct
 from fontTools.misc import psCharStrings
-from fontTools.misc.arrayTools import unionRect
+from fontTools.misc.arrayTools import unionRect, intRect
 from fontTools.misc.textTools import safeEval
 from fontTools.ttLib import TTFont
 from fontTools.ttLib.tables.otBase import OTTableWriter
@@ -2331,7 +2331,7 @@ class TopDict(BaseDict):
 		if bounds == initialBounds:
 			self.FontBBox = self.defaults['FontBBox'][:]
 		else:
-			self.FontBBox = [round(v) for v in bounds]
+			self.FontBBox = list(intRect(bounds))
 
 
 class FontDict(BaseDict):
diff --git a/Tests/cffLib/cffLib_test.py b/Tests/cffLib/cffLib_test.py
index 52825934b..0d1258d02 100644
--- a/Tests/cffLib/cffLib_test.py
+++ b/Tests/cffLib/cffLib_test.py
@@ -19,8 +19,8 @@ class TopDictTest(unittest.TestCase):
             <CharString name="bar"><!-- [0, 0, 200, 200] -->
               0 0 rmoveto 200 hlineto 200 vlineto -200 hlineto endchar
             </CharString>
-            <CharString name="baz"><!-- [-55.5, -55.5, 55.5, 55.5] -->
-              -55.5 -55.5 rmoveto 111 hlineto 111 vlineto -111 hlineto endchar
+            <CharString name="baz"><!-- [-55.1, -55.1, 55.1, 55.1] -->
+              -55.1 -55.1 rmoveto 110.2 hlineto 110.2 vlineto -110.2 hlineto endchar
             </CharString>
         """))