diff --git a/include/nlohmann/detail/exceptions.hpp b/include/nlohmann/detail/exceptions.hpp
index 144bb770c..098d70495 100644
--- a/include/nlohmann/detail/exceptions.hpp
+++ b/include/nlohmann/detail/exceptions.hpp
@@ -222,7 +222,8 @@ class exception : public std::exception
     template<typename BasicJsonType>
     static std::string get_byte_positions(const BasicJsonType* leaf_element)
     {
-        if ((leaf_element->start_pos() != std::string::npos) && (leaf_element->end_pos() != std::string::npos))
+        // a value-initialized iterator has no value (invalid_iterator.212)
+        if (leaf_element != nullptr && leaf_element->start_pos() != std::string::npos && leaf_element->end_pos() != std::string::npos)
         {
             return concat("(bytes ", std::to_string(leaf_element->start_pos()), "-", std::to_string(leaf_element->end_pos()), ") ");
         }
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index 693320ed5..57de40b49 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -5719,7 +5719,8 @@ class exception : public std::exception
     template<typename BasicJsonType>
     static std::string get_byte_positions(const BasicJsonType* leaf_element)
     {
-        if ((leaf_element->start_pos() != std::string::npos) && (leaf_element->end_pos() != std::string::npos))
+        // a value-initialized iterator has no value (invalid_iterator.212)
+        if (leaf_element != nullptr && leaf_element->start_pos() != std::string::npos && leaf_element->end_pos() != std::string::npos)
         {
             return concat("(bytes ", std::to_string(leaf_element->start_pos()), "-", std::to_string(leaf_element->end_pos()), ") ");
         }
diff --git a/tests/src/unit-diagnostic-positions.cpp b/tests/src/unit-diagnostic-positions.cpp
index 9e0625115..6a36e5f7a 100644
--- a/tests/src/unit-diagnostic-positions.cpp
+++ b/tests/src/unit-diagnostic-positions.cpp
@@ -243,3 +243,14 @@ TEST_CASE("values read from a binary format have no positions")
         check_no_positions(j);
     }
 }
+
+TEST_CASE("comparing a value-initialized iterator throws invalid_iterator.212")
+{
+    // such an iterator has no value to take the byte positions from; the
+    // comparison used to dereference the null pointer instead of throwing
+    json j = {1, 2};
+    json::iterator it{};
+    CHECK_THROWS_WITH_AS(it == j.begin(), "[json.exception.invalid_iterator.212] cannot compare iterators of different containers", json::invalid_iterator);
+    CHECK_THROWS_WITH_AS(it < j.begin(), "[json.exception.invalid_iterator.212] cannot compare iterators of different containers", json::invalid_iterator);
+    CHECK_THROWS_WITH_AS(j.begin() == it, "[json.exception.invalid_iterator.212] cannot compare iterators of different containers", json::invalid_iterator);
+}