diff --git a/Lib/fontTools/fontBuilder.py b/Lib/fontTools/fontBuilder.py
index a08442abf..d4b940512 100644
--- a/Lib/fontTools/fontBuilder.py
+++ b/Lib/fontTools/fontBuilder.py
@@ -506,6 +506,7 @@ class FontBuilder(object):
         fontSet = CFFFontSet()
         fontSet.major = 1
         fontSet.minor = 0
+        fontSet.otFont = self.font
         fontSet.fontNames = [psName]
         fontSet.topDictIndex = TopDictIndex()
 
@@ -520,6 +521,7 @@ class FontBuilder(object):
         topDict = TopDict()
         topDict.charset = self.font.getGlyphOrder()
         topDict.Private = private
+        topDict.GlobalSubrs = fontSet.GlobalSubrs
         for key, value in fontInfo.items():
             setattr(topDict, key, value)
         if "FontMatrix" not in fontInfo:
diff --git a/Tests/fontBuilder/fontBuilder_test.py b/Tests/fontBuilder/fontBuilder_test.py
index 8c5127626..bc7837c30 100644
--- a/Tests/fontBuilder/fontBuilder_test.py
+++ b/Tests/fontBuilder/fontBuilder_test.py
@@ -255,6 +255,19 @@ def test_build_cff2(tmpdir):
     _verifyOutput(outPath)
 
 
+def test_build_cff_to_cff2(tmpdir):
+    fb, _, _ = _setupFontBuilder(False, 1000)
+
+    pen = T2CharStringPen(600, None)
+    drawTestGlyph(pen)
+    charString = pen.getCharString()
+    charStrings = {".notdef": charString, "A": charString, "a": charString, ".null": charString}
+    fb.setupCFF("TestFont", {}, charStrings, {})
+
+    from fontTools.varLib.cff import convertCFFtoCFF2
+    convertCFFtoCFF2(fb.font)
+
+
 def test_setupNameTable_no_mac():
     fb, _, nameStrings = _setupFontBuilder(True)
     fb.setupNameTable(nameStrings, mac=False)