diff --git a/include/yaml-cpp/exceptions.h b/include/yaml-cpp/exceptions.h
index e49a32a..25523c9 100644
--- a/include/yaml-cpp/exceptions.h
+++ b/include/yaml-cpp/exceptions.h
@@ -123,7 +123,7 @@ inline const std::string BAD_SUBSCRIPT_WITH_KEY(
 
 inline const std::string BAD_SUBSCRIPT_WITH_KEY(const std::string& key) {
   std::stringstream stream;
-  stream << BAD_SUBSCRIPT << " (key: '" << key << "')";
+  stream << BAD_SUBSCRIPT << " (key: \"" << key << "\")";
   return stream.str();
 }
 
@@ -131,7 +131,7 @@ template <typename T>
 inline const std::string BAD_SUBSCRIPT_WITH_KEY(
     const T& key, typename enable_if<is_numeric<T>>::type* = 0) {
   std::stringstream stream;
-  stream << BAD_SUBSCRIPT << " (key: '" << key << "')";
+  stream << BAD_SUBSCRIPT << " (key: \"" << key << "\")";
   return stream.str();
 }
 
@@ -140,7 +140,7 @@ inline const std::string INVALID_NODE_WITH_KEY(const std::string& key) {
   if (key.empty()) {
     return INVALID_NODE;
   }
-  stream << "invalid node - first invalid key: '" << key << "'";
+  stream << "invalid node; first invalid key: \"" << key << "\"";
   return stream.str();
 }
 }
diff --git a/include/yaml-cpp/node/impl.h b/include/yaml-cpp/node/impl.h
index 52f6f5d..60120cf 100644
--- a/include/yaml-cpp/node/impl.h
+++ b/include/yaml-cpp/node/impl.h
@@ -374,25 +374,9 @@ inline typename to_value_t<T>::return_type to_value(const T& t) {
 }
 }
 
-template<typename Key, bool Streamable>
-struct key_to_string_impl {
-  static std::string impl(const Key& key) {
-    std::stringstream ss;
-    ss << key;
-    return ss.str();
-  }
-};
-
-template<typename Key>
-struct key_to_string_impl<Key, false> {
-  static std::string impl(const Key&) {
-    return std::string();
-  }
-};
-
 template<typename Key>
 std::string key_to_string(const Key& key) {
-  return key_to_string_impl<Key, is_streamable<std::stringstream, Key>::value>().impl(key);
+  return streamable_to_string<Key, is_streamable<std::stringstream, Key>::value>().impl(key);
 }
 
 // indexing
diff --git a/include/yaml-cpp/node/node.h b/include/yaml-cpp/node/node.h
index cc54d17..49af58e 100644
--- a/include/yaml-cpp/node/node.h
+++ b/include/yaml-cpp/node/node.h
@@ -132,7 +132,7 @@ class YAML_CPP_API Node {
 
  private:
   bool m_isValid;
-  // string representation of invalid key, if the node is invalid
+  // String representation of invalid key, if the node is invalid.
   std::string m_invalidKey;
   mutable detail::shared_memory_holder m_pMemory;
   mutable detail::node* m_pNode;
diff --git a/include/yaml-cpp/traits.h b/include/yaml-cpp/traits.h
index e7079d7..f3cda64 100644
--- a/include/yaml-cpp/traits.h
+++ b/include/yaml-cpp/traits.h
@@ -9,6 +9,8 @@
 
 #include <type_traits>
 #include <utility>
+#include <string>
+#include <sstream>
 
 namespace YAML {
 template <typename>
@@ -104,7 +106,7 @@ struct disable_if : public disable_if_c<Cond::value, T> {};
 }
 
 template <typename S, typename T>
-class is_streamable {
+struct is_streamable {
   template <typename SS, typename TT>
   static auto test(int)
       -> decltype(std::declval<SS&>() << std::declval<TT>(), std::true_type());
@@ -112,8 +114,22 @@ class is_streamable {
   template <typename, typename>
   static auto test(...) -> std::false_type;
 
- public:
   static const bool value = decltype(test<S, T>(0))::value;
 };
 
+template<typename Key, bool Streamable>
+struct streamable_to_string {
+  static std::string impl(const Key& key) {
+    std::stringstream ss;
+    ss << key;
+    return ss.str();
+  }
+};
+
+template<typename Key>
+struct streamable_to_string<Key, false> {
+  static std::string impl(const Key&) {
+    return std::string();
+  }
+};
 #endif  // TRAITS_H_62B23520_7C8E_11DE_8A39_0800200C9A66
diff --git a/test/integration/error_messages_test.cpp b/test/integration/error_messages_test.cpp
index a9d09c8..64ab6b9 100644
--- a/test/integration/error_messages_test.cpp
+++ b/test/integration/error_messages_test.cpp
@@ -1,4 +1,3 @@
-#include "specexamples.h"
 #include "yaml-cpp/yaml.h"  // IWYU pragma: keep
 
 #include "gtest/gtest.h"
@@ -14,15 +13,19 @@
 namespace YAML {
 namespace {
 
-TEST(ErrorMessageTest, Ex9_1_BadSubscriptErrorMessage) {
-  Node doc = Load(ex9_1);
+TEST(ErrorMessageTest, BadSubscriptErrorMessage) {
+  const char *example_yaml = "first:\n"
+                             "   second: 1\n"
+                             "   third: 2\n";
+
+  Node doc = Load(example_yaml);
 
   // Test that printable key is part of error message
   EXPECT_THROW_EXCEPTION(YAML::BadSubscript, doc["first"]["second"]["fourth"],
-                         "operator[] call on a scalar (key: 'fourth')");
+                         "operator[] call on a scalar (key: \"fourth\")");
   
   EXPECT_THROW_EXCEPTION(YAML::BadSubscript, doc["first"]["second"][37],
-                         "operator[] call on a scalar (key: '37')");
+                         "operator[] call on a scalar (key: \"37\")");
 
 
   // Non-printable key is not included in error message
@@ -35,14 +38,18 @@ TEST(ErrorMessageTest, Ex9_1_BadSubscriptErrorMessage) {
 }
 
 TEST(ErrorMessageTest, Ex9_1_InvalidNodeErrorMessage) {
-  const Node doc = Load(ex9_1);
+  const char *example_yaml = "first:\n"
+                             "   second: 1\n"
+                             "   third: 2\n";
+
+  const Node doc = Load(example_yaml);
 
   // Test that printable key is part of error message
   EXPECT_THROW_EXCEPTION(YAML::InvalidNode, doc["first"]["fourth"].as<int>(),
-                         "invalid node - first invalid key: 'fourth'");
+                         "invalid node; first invalid key: \"fourth\"");
   
   EXPECT_THROW_EXCEPTION(YAML::InvalidNode, doc["first"][37].as<int>(),
-                         "invalid node - first invalid key: '37'");
+                         "invalid node; first invalid key: \"37\"");
  
   // Non-printable key is not included in error message
   EXPECT_THROW_EXCEPTION(YAML::InvalidNode,
diff --git a/test/specexamples.h b/test/specexamples.h
index e4e85ef..3c81c77 100644
--- a/test/specexamples.h
+++ b/test/specexamples.h
@@ -843,9 +843,4 @@ const char *ex8_22 =
     " - nested\n"
     "mapping: !!map\n"
     " foo: bar\n";
-
-const char *ex9_1 =
-    "first:\n"
-    "   second: 1\n"
-    "   third: 2\n";
 }