diff --git a/source/utf8.h b/source/utf8.h
index d8c58d9..82b13f5 100644
--- a/source/utf8.h
+++ b/source/utf8.h
@@ -31,16 +31,4 @@ DEALINGS IN THE SOFTWARE.
 #include "utf8/checked.h"
 #include "utf8/unchecked.h"
 
-// Determine whether to include C++ 11 specific header
-// If the user defines UTF_CPP_CPLUSPLUS, use that.
-// Otherwise, trust the unreliable predefined macro __cplusplus
-
-#if !defined UTF_CPP_CPLUSPLUS
-    #define UTF_CPP_CPLUSPLUS __cplusplus
-#endif
-
-#if UTF_CPP_CPLUSPLUS >= 201103L // C++ 11 or later
-#include "utf8/cpp11.h"
-#endif // C++ 11 or later
-
 #endif // header guard
diff --git a/source/utf8/checked.h b/source/utf8/checked.h
index c31861e..29b7957 100644
--- a/source/utf8/checked.h
+++ b/source/utf8/checked.h
@@ -320,5 +320,9 @@ namespace utf8
 
 } // namespace utf8
 
+#if UTF_CPP_CPLUSPLUS >= 201103L // C++ 11 or later
+#include "utf8/cpp11.h"
+#endif // C++ 11 or later
+
 #endif //header guard
 
diff --git a/source/utf8/core.h b/source/utf8/core.h
index e007ca1..17160f1 100644
--- a/source/utf8/core.h
+++ b/source/utf8/core.h
@@ -30,6 +30,15 @@ DEALINGS IN THE SOFTWARE.
 
 #include <iterator>
 
+// Determine the C++ standard version.
+// If the user defines UTF_CPP_CPLUSPLUS, use that.
+// Otherwise, trust the unreliable predefined macro __cplusplus
+
+#if !defined UTF_CPP_CPLUSPLUS
+    #define UTF_CPP_CPLUSPLUS __cplusplus
+#endif
+
+
 namespace utf8
 {
     // The typedefs for 8-bit, 16-bit and 32-bit unsigned integers