diff --git a/libqpdf/SparseOHArray.cc b/libqpdf/SparseOHArray.cc
index c8aaefa8..972376b1 100644
--- a/libqpdf/SparseOHArray.cc
+++ b/libqpdf/SparseOHArray.cc
@@ -57,7 +57,7 @@ SparseOHArray::remove_last()
 void
 SparseOHArray::releaseResolved()
 {
-    for (auto iter: this->elements)
+    for (auto& iter: this->elements)
     {
 	QPDFObjectHandle::ReleaseResolver::releaseResolved(iter.second);
     }
diff --git a/libtests/cxx11.cc b/libtests/cxx11.cc
index 91ed7b15..ba4525ed 100644
--- a/libtests/cxx11.cc
+++ b/libtests/cxx11.cc
@@ -105,7 +105,7 @@ void do_iteration()
     std::vector<int> v = { 1, 2, 3, 4 };
     assert(v.size() == 4);
     int sum = 0;
-    for (auto i: v)
+    for (auto& i: v)
     {
         sum += i;
     }
diff --git a/qpdf/fix-qdf.cc b/qpdf/fix-qdf.cc
index c50f7b5a..c83b495a 100644
--- a/qpdf/fix-qdf.cc
+++ b/qpdf/fix-qdf.cc
@@ -110,7 +110,7 @@ QdfFixer::processLines(std::list<std::string>& lines)
     static std::regex re_dict_end("^>>\n$");
 
     lineno = 0;
-    for (auto line: lines)
+    for (auto const& line: lines)
     {
         ++lineno;
         last_offset = offset;
@@ -163,7 +163,7 @@ QdfFixer::processLines(std::list<std::string>& lines)
                 // index. Make sure we get at least 1 byte even if
                 // there are no object streams.
                 int max_objects = 1;
-                for (auto e: xref)
+                for (auto const& e: xref)
                 {
                     if ((e.getType() == 2) &&
                         (e.getObjStreamIndex() > max_objects))
@@ -258,7 +258,7 @@ QdfFixer::processLines(std::list<std::string>& lines)
                 writeBinary(0, 1);
                 writeBinary(0, xref_f1_nbytes);
                 writeBinary(0, xref_f2_nbytes);
-                for (auto x: xref)
+                for (auto const& x: xref)
                 {
                     unsigned long long f1 = 0;
                     unsigned long long f2 = 0;
@@ -321,7 +321,7 @@ QdfFixer::processLines(std::list<std::string>& lines)
         {
             auto n = xref.size();
             std::cout << "0 " << 1 + n << "\n0000000000 65535 f \n";
-            for (auto e: xref)
+            for (auto const& e: xref)
             {
                 std::cout << QUtil::int_to_string(e.getOffset(), 10)
                           << " 00000 n \n";
@@ -410,12 +410,12 @@ QdfFixer::writeOstream()
     std::cout << dict_data
               << "stream\n"
               << offsets;
-    for (auto o: ostream)
+    for (auto const& o: ostream)
     {
 	std::cout << o;
     }
 
-    for (auto o: ostream_discarded)
+    for (auto const& o: ostream_discarded)
     {
 	offset -= QIntC::to_offset(o.length());
     }
diff --git a/qpdf/qpdf.cc b/qpdf/qpdf.cc
index 35267e85..02a95c73 100644
--- a/qpdf/qpdf.cc
+++ b/qpdf/qpdf.cc
@@ -3693,7 +3693,7 @@ static void do_json_objectinfo(QPDF& pdf, Options& o, JSON& j)
     std::set<QPDFObjGen> wanted_og = get_wanted_json_objects(o);
     JSON j_objectinfo = j.addDictionaryMember(
         "objectinfo", JSON::makeDictionary());
-    for (auto obj: pdf.getAllObjects())
+    for (auto& obj: pdf.getAllObjects())
     {
         if (all_objects || wanted_og.count(obj.getObjGen()))
         {
@@ -4922,7 +4922,7 @@ static bool should_remove_unreferenced_resources(QPDF& pdf, Options& o)
             }
             if (xobject.isDictionary())
             {
-                for (auto k: xobject.getKeys())
+                for (auto const& k: xobject.getKeys())
                 {
                     QPDFObjectHandle xobj = xobject.getKey(k);
                     if (xobj.isStream() &&