diff --git a/date.h b/date.h
index 4df3fa1..ef3b586 100644
--- a/date.h
+++ b/date.h
@@ -60,15 +60,15 @@ namespace date
 // MSVC's constexpr support is still a WIP, even in VS2015.
 // Fall back to a lesser mode to support it.
 // TODO: Remove this or retest later once MSVC's constexpr improves.
-#if defined(_MSC_VER) && ! defined(__clang__)
-// MS cl compiler.
+#if defined(_MSC_VER) && _MSC_VER <= 1900 && ! defined(__clang__)
+// MS cl compiler pre VS2017
 #  define CONSTDATA const
 #  define CONSTCD11
 #  define CONSTCD14
 #  define NOEXCEPT _NOEXCEPT
 #elif __cplusplus >= 201402
 // C++14
-#  define CONSTDATA constexpr
+#  define CONSTDATA constexpr const
 #  define CONSTCD11 constexpr
 #  define CONSTCD14 constexpr
 #  define NOEXCEPT noexcept
diff --git a/tz.cpp b/tz.cpp
index d465481..17c2795 100644
--- a/tz.cpp
+++ b/tz.cpp
@@ -724,7 +724,7 @@ static
 unsigned
 parse_dow(std::istream& in)
 {
-    const char*const dow_names[] =
+    CONSTDATA char*const dow_names[] =
         {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};
     auto s = parse3(in);
     auto dow = std::find(std::begin(dow_names), std::end(dow_names), s) - dow_names;
@@ -737,7 +737,7 @@ static
 unsigned
 parse_month(std::istream& in)
 {
-    const char*const month_names[] =
+    CONSTDATA char*const month_names[] =
         {"Jan", "Feb", "Mar", "Apr", "May", "Jun",
          "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};
     auto s = parse3(in);
@@ -2800,7 +2800,7 @@ init_tzdb()
     db.version = get_version(path);
 #endif  // !AUTO_DOWNLOAD
 
-    CONSTDATA const char* files[] =
+    CONSTDATA char*const files[] =
     {
         "africa", "antarctica", "asia", "australasia", "backward", "etcetera", "europe",
         "pacificnew", "northamerica", "southamerica", "systemv", "leapseconds"