diff --git a/tests/test_find.cpp b/tests/test_find.cpp
index 4d1ce3c..d11ddd7 100644
--- a/tests/test_find.cpp
+++ b/tests/test_find.cpp
@@ -19,11 +19,14 @@
 
 namespace toml
 {
+inline namespace TOML11_INLINE_VERSION_NAMESPACE
+{
 namespace detail
 {
 std::tm localtime_s(const std::time_t* src);
 std::tm gmtime_s(const std::time_t* src);
 } // detail
+} // TOML11_INLINE_VERSION_NAMESPACE
 } // toml
 
 TEST_CASE("testing toml::find with toml type")
diff --git a/tests/test_get.cpp b/tests/test_get.cpp
index 137ce0c..99a8a52 100644
--- a/tests/test_get.cpp
+++ b/tests/test_get.cpp
@@ -19,11 +19,14 @@
 
 namespace toml
 {
+inline namespace TOML11_INLINE_VERSION_NAMESPACE
+{
 namespace detail
 {
 std::tm localtime_s(const std::time_t* src);
 std::tm gmtime_s(const std::time_t* src);
 } // detail
+} // TOML11_INLINE_VERSION_NAMESPACE
 } // toml
 
 TEST_CASE("testing toml::get with toml types")
diff --git a/tests/test_user_defined_conversion.cpp b/tests/test_user_defined_conversion.cpp
index 9f27b63..293eb13 100644
--- a/tests/test_user_defined_conversion.cpp
+++ b/tests/test_user_defined_conversion.cpp
@@ -76,6 +76,8 @@ struct corge
 
 namespace toml
 {
+inline namespace TOML11_INLINE_VERSION_NAMESPACE
+{
 template<>
 struct from<extlib::foo>
 {
@@ -113,6 +115,7 @@ struct into<extlib::qux>
         return toml::basic_value<TC>(typename toml::basic_value<TC>::table_type{{"a", f.a}, {"b", f.b}});
     }
 };
+} // TOML11_INLINE_VERSION_NAMESPACE
 } // toml
 
 // ---------------------------------------------------------------------------
@@ -167,6 +170,8 @@ struct foobar
 
 namespace toml
 {
+inline namespace TOML11_INLINE_VERSION_NAMESPACE
+{
 template<>
 struct from<extlib2::foo>
 {
@@ -209,6 +214,7 @@ struct into<extlib2::qux>
         };
     }
 };
+} // TOML11_INLINE_VERSION_NAMESPACE
 } // toml
 
 // ---------------------------------------------------------------------------
diff --git a/tests/utility.cpp b/tests/utility.cpp
index 82589cc..5363f16 100644
--- a/tests/utility.cpp
+++ b/tests/utility.cpp
@@ -25,6 +25,8 @@ void test_scan_failure(const toml::detail::scanner_base& s,
 
 namespace toml
 {
+inline namespace TOML11_INLINE_VERSION_NAMESPACE
+{
 
 std::ostream& operator<<(std::ostream& os, const integer_format_info& fmt)
 {
@@ -102,4 +104,5 @@ std::ostream& operator<<(std::ostream& os, const table_format_info& fmt)
     return os;
 }
 
+} // TOML11_INLINE_VERSION_NAMESPACE
 } // toml
diff --git a/tests/utility.hpp b/tests/utility.hpp
index 06c05e9..2bbd095 100644
--- a/tests/utility.hpp
+++ b/tests/utility.hpp
@@ -86,6 +86,8 @@ void toml11_test_parse_failure(F fn, std::string in, toml::detail::context<TC> c
 
 namespace toml
 {
+inline namespace TOML11_INLINE_VERSION_NAMESPACE
+{
 std::ostream& operator<<(std::ostream& os, const integer_format_info&);
 std::ostream& operator<<(std::ostream& os, const floating_format_info&);
 std::ostream& operator<<(std::ostream& os, const string_format_info&);
@@ -96,5 +98,6 @@ std::ostream& operator<<(std::ostream& os, const local_time_format_info&);
 std::ostream& operator<<(std::ostream& os, const array_format_info&);
 std::ostream& operator<<(std::ostream& os, const table_format_info&);
 
+} // TOML11_INLINE_VERSION_NAMESPACE
 } // toml
 #endif// TOML11_TEST_UTILITY_HPP