diff --git a/libqpdf/Pl_StdioFile.cc b/libqpdf/Pl_StdioFile.cc
index e87de10c..bd56ac61 100644
--- a/libqpdf/Pl_StdioFile.cc
+++ b/libqpdf/Pl_StdioFile.cc
@@ -1,3 +1,4 @@
+#include <qpdf/qpdf-config.h>  // include first for large file support
 #include <qpdf/Pl_StdioFile.hh>
 #include <qpdf/QUtil.hh>
 #include <stdexcept>
diff --git a/libqpdf/QPDF.cc b/libqpdf/QPDF.cc
index 743ba93b..b4bad4f2 100644
--- a/libqpdf/QPDF.cc
+++ b/libqpdf/QPDF.cc
@@ -1,3 +1,4 @@
+#include <qpdf/qpdf-config.h>  // include first for large file support
 #include <qpdf/QPDF.hh>
 
 #include <vector>
diff --git a/libqpdf/QPDFWriter.cc b/libqpdf/QPDFWriter.cc
index 22d0b6ea..564133e3 100644
--- a/libqpdf/QPDFWriter.cc
+++ b/libqpdf/QPDFWriter.cc
@@ -1,3 +1,4 @@
+#include <qpdf/qpdf-config.h>  // include first for large file support
 #include <qpdf/QPDFWriter.hh>
 
 #include <assert.h>
diff --git a/qpdf/test_large_file.cc b/qpdf/test_large_file.cc
index c1ee4060..880877f4 100644
--- a/qpdf/test_large_file.cc
+++ b/qpdf/test_large_file.cc
@@ -1,3 +1,9 @@
+// NOTE: This test program doesn't do anything special to enable large
+// file support.  This is important since it verifies that programs
+// don't have to do anything special -- all the work is done
+// internally by the library as long as they don't do their own file
+// I/O.
+
 #include <qpdf/QPDF.hh>
 #include <qpdf/QPDFWriter.hh>
 #include <qpdf/QPDFObjectHandle.hh>