diff --git a/libqpdf/NNTree.cc b/libqpdf/NNTree.cc
index 2257154..6d68575 100644
--- a/libqpdf/NNTree.cc
+++ b/libqpdf/NNTree.cc
@@ -12,17 +12,17 @@
 #include <utility>
 
 static std::string
-get_description(QPDFObjectHandle& node)
+get_description(QPDFObjectHandle const& node)
 {
     std::string result("Name/Number tree node");
-    if (node.isIndirect()) {
+    if (node.indirect()) {
         result += " (object " + std::to_string(node.getObjectID()) + ")";
     }
     return result;
 }
 
 void
-NNTreeImpl::warn(QPDFObjectHandle& node, std::string const& msg)
+NNTreeImpl::warn(QPDFObjectHandle const& node, std::string const& msg)
 {
     qpdf.warn(qpdf_e_damaged_pdf, get_description(node), 0, msg);
     if (++error_count > 5 && qpdf.reconstructed_xref()) {
@@ -31,7 +31,7 @@ NNTreeImpl::warn(QPDFObjectHandle& node, std::string const& msg)
 }
 
 void
-NNTreeImpl::error(QPDFObjectHandle& node, std::string const& msg)
+NNTreeImpl::error(QPDFObjectHandle const& node, std::string const& msg)
 {
     throw QPDFExc(qpdf_e_damaged_pdf, qpdf.getFilename(), get_description(node), 0, msg);
 }
@@ -701,22 +701,19 @@ NNTreeImpl::last()
 }
 
 int
-NNTreeImpl::withinLimits(QPDFObjectHandle key, QPDFObjectHandle node)
+NNTreeImpl::withinLimits(QPDFObjectHandle const& key, QPDFObjectHandle const& node)
 {
-    int result = 0;
     auto limits = node.getKey("/Limits");
-    if (limits.isArray() && (limits.getArrayNItems() >= 2) &&
-        details.keyValid(limits.getArrayItem(0)) && details.keyValid(limits.getArrayItem(1))) {
-        if (details.compareKeys(key, limits.getArrayItem(0)) < 0) {
-            result = -1;
-        } else if (details.compareKeys(key, limits.getArrayItem(1)) > 0) {
-            result = 1;
-        }
-    } else {
-        QTC::TC("qpdf", "NNTree missing limits");
+    if (!(limits.size() >= 2 && details.keyValid(limits[0]) && details.keyValid(limits[1]))) {
         error(node, "node is missing /Limits");
     }
-    return result;
+    if (details.compareKeys(key, limits[0]) < 0) {
+        return -1;
+    }
+    if (details.compareKeys(key, limits[1]) > 0) {
+        return 1;
+    }
+    return 0;
 }
 
 int
diff --git a/libqpdf/qpdf/NNTree.hh b/libqpdf/qpdf/NNTree.hh
index c904703..af50bbf 100644
--- a/libqpdf/qpdf/NNTree.hh
+++ b/libqpdf/qpdf/NNTree.hh
@@ -111,7 +111,7 @@ class NNTreeImpl
   private:
     void repair();
     iterator findInternal(QPDFObjectHandle const& key, bool return_prev_if_not_found = false);
-    int withinLimits(QPDFObjectHandle key, QPDFObjectHandle node);
+    int withinLimits(QPDFObjectHandle const& key, QPDFObjectHandle const& node);
     int binarySearch(
         QPDFObjectHandle key,
         QPDFObjectHandle items,
@@ -120,8 +120,8 @@ class NNTreeImpl
         int (NNTreeImpl::*compare)(QPDFObjectHandle& key, QPDFObjectHandle& arr, int item));
     int compareKeyItem(QPDFObjectHandle& key, QPDFObjectHandle& items, int idx);
     int compareKeyKid(QPDFObjectHandle& key, QPDFObjectHandle& items, int idx);
-    void warn(QPDFObjectHandle& node, std::string const& msg);
-    void error(QPDFObjectHandle& node, std::string const& msg);
+    void warn(QPDFObjectHandle const& node, std::string const& msg);
+    void error(QPDFObjectHandle const& node, std::string const& msg);
 
     NNTreeDetails const& details;
     QPDF& qpdf;
diff --git a/qpdf/qpdf.testcov b/qpdf/qpdf.testcov
index a12d39a..0af3b37 100644
--- a/qpdf/qpdf.testcov
+++ b/qpdf/qpdf.testcov
@@ -536,7 +536,6 @@ NNTree split items 0
 NNTree split second half item 0
 NNTree split parent 0
 NNTree split second half kid 0
-NNTree missing limits 0
 NNTree node is not a dictionary 0
 NNTree limits didn't change 0
 NNTree increment end() 0