diff --git a/libqpdf/NNTree.cc b/libqpdf/NNTree.cc
index 02881e99..fa054794 100644
--- a/libqpdf/NNTree.cc
+++ b/libqpdf/NNTree.cc
@@ -591,7 +591,7 @@ NNTreeIterator::deepen(QPDFObjectHandle node, bool first, bool allow_empty)
     bool failed = false;
 
     QPDFObjGen::set seen;
-    for (auto i: this->path) {
+    for (auto const& i: this->path) {
         seen.add(i.node);
     }
     while (!failed) {
diff --git a/libqpdf/QPDFAcroFormDocumentHelper.cc b/libqpdf/QPDFAcroFormDocumentHelper.cc
index 83feb358..5a54bf75 100644
--- a/libqpdf/QPDFAcroFormDocumentHelper.cc
+++ b/libqpdf/QPDFAcroFormDocumentHelper.cc
@@ -70,7 +70,7 @@ QPDFAcroFormDocumentHelper::addAndRenameFormFields(std::vector<QPDFObjectHandle>
         if (seen.add(obj)) {
             auto kids = obj.getKey("/Kids");
             if (kids.isArray()) {
-                for (auto kid: kids.aitems()) {
+                for (auto const& kid: kids.aitems()) {
                     queue.push_back(kid);
                 }
             }
@@ -104,7 +104,7 @@ QPDFAcroFormDocumentHelper::addAndRenameFormFields(std::vector<QPDFObjectHandle>
         }
     }
 
-    for (auto i: fields) {
+    for (auto const& i: fields) {
         addFormField(i);
     }
 }
@@ -1018,7 +1018,7 @@ QPDFAcroFormDocumentHelper::fixCopiedAnnotations(
     to_page.replaceKey("/Annots", QPDFObjectHandle::newArray(new_annots));
     addAndRenameFormFields(new_fields);
     if (added_fields) {
-        for (auto f: new_fields) {
+        for (auto const& f: new_fields) {
             added_fields->insert(f.getObjGen());
         }
     }
diff --git a/libqpdf/QPDFJob.cc b/libqpdf/QPDFJob.cc
index c33c4b70..3f3bcbb1 100644
--- a/libqpdf/QPDFJob.cc
+++ b/libqpdf/QPDFJob.cc
@@ -894,7 +894,7 @@ QPDFJob::doListAttachments(QPDF& pdf)
                     v << "    " << i2.first << " -> " << i2.second << "\n";
                 }
                 v << "  all data streams:\n";
-                for (auto i2: efoh->getEmbeddedFileStreams().ditems()) {
+                for (auto const& i2: efoh->getEmbeddedFileStreams().ditems()) {
                     auto efs = QPDFEFStreamObjectHelper(i2.second);
                     v << "    " << i2.first << " -> "
                       << efs.getObjectHandle().getObjGen().unparse(',') << "\n";
@@ -1329,7 +1329,7 @@ QPDFJob::doJSONAttachments(Pipeline* p, bool& first, QPDF& pdf)
             j_names.addDictionaryMember(i2.first, JSON::makeString(i2.second));
         }
         auto j_streams = j_details.addDictionaryMember("streams", JSON::makeDictionary());
-        for (auto i2: fsoh->getEmbeddedFileStreams().ditems()) {
+        for (auto const& i2: fsoh->getEmbeddedFileStreams().ditems()) {
             auto efs = QPDFEFStreamObjectHelper(i2.second);
             auto j_stream = j_streams.addDictionaryMember(i2.first, JSON::makeDictionary());
             j_stream.addDictionaryMember(
diff --git a/libqpdf/QPDFObjectHandle.cc b/libqpdf/QPDFObjectHandle.cc
index 9ec87f79..3ce748b0 100644
--- a/libqpdf/QPDFObjectHandle.cc
+++ b/libqpdf/QPDFObjectHandle.cc
@@ -1048,7 +1048,7 @@ QPDFObjectHandle::makeResourcesIndirect(QPDF& owning_qpdf)
         if (!sub.isDictionary()) {
             continue;
         }
-        for (auto i2: sub.ditems()) {
+        for (auto const& i2: sub.ditems()) {
             std::string const& key = i2.first;
             QPDFObjectHandle val = i2.second;
             if (!val.isIndirect()) {
@@ -1069,7 +1069,7 @@ QPDFObjectHandle::mergeResources(
 
     auto make_og_to_name = [](QPDFObjectHandle& dict,
                               std::map<QPDFObjGen, std::string>& og_to_name) {
-        for (auto i: dict.ditems()) {
+        for (auto const& i: dict.ditems()) {
             if (i.second.isIndirect()) {
                 og_to_name[i.second.getObjGen()] = i.first;
             }
@@ -1078,7 +1078,7 @@ QPDFObjectHandle::mergeResources(
 
     // This algorithm is described in comments in QPDFObjectHandle.hh
     // above the declaration of mergeResources.
-    for (auto o_top: other.ditems()) {
+    for (auto const& o_top: other.ditems()) {
         std::string const& rtype = o_top.first;
         QPDFObjectHandle other_val = o_top.second;
         if (hasKey(rtype)) {
@@ -1095,7 +1095,7 @@ QPDFObjectHandle::mergeResources(
                 std::set<std::string> rnames;
                 int min_suffix = 1;
                 bool initialized_maps = false;
-                for (auto ov_iter: other_val.ditems()) {
+                for (auto const& ov_iter: other_val.ditems()) {
                     std::string const& key = ov_iter.first;
                     QPDFObjectHandle rval = ov_iter.second;
                     if (!this_val.hasKey(key)) {
diff --git a/qpdf/test_driver.cc b/qpdf/test_driver.cc
index 6fdacf1b..b2ed825d 100644
--- a/qpdf/test_driver.cc
+++ b/qpdf/test_driver.cc
@@ -2576,7 +2576,7 @@ test_76(QPDF& pdf, char const* arg2)
     assert(efs2.getSubtype() == "text/plain");
     assert(QUtil::hex_encode(efs2.getChecksum()) == "2fce9c8228e360ba9b04a1bd1bf63d6b");
 
-    for (auto iter: efdh.getEmbeddedFiles()) {
+    for (auto const& iter: efdh.getEmbeddedFiles()) {
         std::cout << iter.first << " -> " << iter.second->getFilename() << std::endl;
     }
     assert(efdh.getEmbeddedFile("att1")->getFilename() == "att1.txt");