diff --git a/include/stdex/base64.hpp b/include/stdex/base64.hpp
index 66f0bae1a..f7f56d00d 100644
--- a/include/stdex/base64.hpp
+++ b/include/stdex/base64.hpp
@@ -15,14 +15,20 @@
 namespace stdex
 {
 	/// \cond internal
-	inline const char base64_enc_lookup[64] = {
+#if _HAS_CXX17
+	inline
+#endif
+	const char base64_enc_lookup[64] = {
 		'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',
 		'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',
 		'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',
 		'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'
 	};
 
-	inline const uint8_t base64_dec_lookup[256] = {
+#if _HAS_CXX17
+	inline
+#endif
+	const uint8_t base64_dec_lookup[256] = {
 	/*           0    1    2    3    4    5    6    7    8    9    A    B    C    D    E    F  */
 	/* 0 */    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
 	/* 1 */    255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255,
diff --git a/include/stdex/sgml_unicode.hpp b/include/stdex/sgml_unicode.hpp
index f976743ac..4f26e2923 100644
--- a/include/stdex/sgml_unicode.hpp
+++ b/include/stdex/sgml_unicode.hpp
@@ -13,7 +13,10 @@ namespace stdex
 		wchar_t unicode[3]; ///< Unicode string representation
 	};
 
-	inline const sgml_unicode_pair sgml_unicode[] = {
+#if _HAS_CXX17
+	inline
+#endif
+	const sgml_unicode_pair sgml_unicode[] = {
 		{ "AElig", L"\u00c6" },
 		{ "Aacgr", L"\u0386" },
 		{ "Aacute", L"\u00c1" },
@@ -1551,7 +1554,10 @@ namespace stdex
 		{ "zwnj", L"\u200c" },
 	};
 
-	inline const size_t unicode_sgml[] = {
+#if _HAS_CXX17
+	inline
+#endif
+	const size_t unicode_sgml[] = {
 		0x5b6,
 		0x48d,
 		0x30d,
diff --git a/include/stdex/sys_info.hpp b/include/stdex/sys_info.hpp
index 194ede03b..6f0b05f46 100644
--- a/include/stdex/sys_info.hpp
+++ b/include/stdex/sys_info.hpp
@@ -48,7 +48,10 @@ namespace stdex
 	///
 	/// System information
 	///
-	inline const struct sys_info_t
+#if _HAS_CXX17
+	inline
+#endif
+	const struct sys_info_t
 	{
 		///
 		/// The platform this process was compiled for