diff --git a/libqpdf/QPDFStreamFilter.cc b/libqpdf/QPDFStreamFilter.cc
index 66a2f76..a4949de 100644
--- a/libqpdf/QPDFStreamFilter.cc
+++ b/libqpdf/QPDFStreamFilter.cc
@@ -1,9 +1,11 @@
 #include <qpdf/QPDFStreamFilter.hh>
 
+#include <qpdf/QPDFObjectHandle_private.hh>
+
 bool
 QPDFStreamFilter::setDecodeParms(QPDFObjectHandle decode_parms)
 {
-    return decode_parms.isNull();
+    return decode_parms.null();
 }
 
 bool
diff --git a/libqpdf/SF_FlateLzwDecode.cc b/libqpdf/SF_FlateLzwDecode.cc
index bd5454d..e71cb24 100644
--- a/libqpdf/SF_FlateLzwDecode.cc
+++ b/libqpdf/SF_FlateLzwDecode.cc
@@ -5,12 +5,13 @@
 #include <qpdf/Pl_PNGFilter.hh>
 #include <qpdf/Pl_TIFFPredictor.hh>
 #include <qpdf/QIntC.hh>
+#include <qpdf/QPDFObjectHandle_private.hh>
 #include <qpdf/QTC.hh>
 
 bool
 SF_FlateLzwDecode::setDecodeParms(QPDFObjectHandle decode_parms)
 {
-    if (decode_parms.isNull()) {
+    if (decode_parms.null()) {
         return true;
     }