3 files changed, 33 insertions, 20 deletions

diff --git a/config/config.h.in b/config/config.h.in
index 56d46e9f14..3f2f68da83 100644
--- a/config/config.h.in
+++ b/config/config.h.in
@@ -27,7 +27,6 @@
 #cmakedefine HAVE_LOCALE_H
 #cmakedefine HAVE_NL_LANGINFO_CODESET
 #cmakedefine HAVE_NL_MSG_CAT_CNTR
-#cmakedefine HAVE_PUTENV_S
 #cmakedefine HAVE_PWD_H
 #cmakedefine HAVE_READLINK
 #cmakedefine HAVE_UV_TRANSLATE_SYS_ERROR
diff --git a/src/nvim/os/env.c b/src/nvim/os/env.c
index c6794e4be5..6cf48eb814 100644
--- a/src/nvim/os/env.c
+++ b/src/nvim/os/env.c
@@ -52,29 +52,29 @@ int os_setenv(const char *name, const char *value, int overwrite)
   FUNC_ATTR_NONNULL_ALL
 {
 #ifdef WIN32
-  size_t envbuflen = strlen(name) + strlen(value) + 2;
-  char *envbuf = xmalloc(envbuflen);
-  snprintf(envbuf, envbuflen, "%s=%s", name, value);
-
-  wchar_t *p;
-  utf8_to_utf16(envbuf, &p);
-  xfree(envbuf);
-  if (p == NULL) {
+  if (!overwrite && os_getenv(name) != NULL) {
+    return 0;
+  }
+  wchar_t *wname;
+  utf8_to_utf16(name, &wname);
+  if (wname == NULL) {
+    return -1;
+  }
+  wchar_t *wvalue;
+  utf8_to_utf16(value, &wvalue);
+  if (wvalue == NULL) {
+    return -1;
+  }
+  int rv = (int)_wputenv_s(wname, wvalue);
+  xfree(wname);  // Unlike unix putenv(), we can free after _wputenv_s().
+  xfree(wvalue);
+  if (rv != 0) {
+    ELOG("_wputenv_s failed: %d: %s", rv, uv_strerror(rv));
     return -1;
   }
-  _wputenv(p);
-  xfree(p);  // Unlike Unix systems, we can free the string for _wputenv().
   return 0;
 #elif defined(HAVE_SETENV)
   return setenv(name, value, overwrite);
-#elif defined(HAVE_PUTENV_S)
-  if (!overwrite && os_getenv(name) != NULL) {
-    return 0;
-  }
-  if (_putenv_s(name, value) == 0) {
-    return 0;
-  }
-  return -1;
 #else
 # error "This system has no implementation available for os_setenv()"
 #endif
diff --git a/test/functional/eval/let_spec.lua b/test/functional/eval/let_spec.lua
index 1bd3405698..050cff3c22 100644
--- a/test/functional/eval/let_spec.lua
+++ b/test/functional/eval/let_spec.lua
@@ -2,13 +2,15 @@ local helpers = require('test.functional.helpers')(after_each)
 
 local eq = helpers.eq
 local clear = helpers.clear
+local command = helpers.command
+local eval = helpers.eval
 local meths = helpers.meths
 local redir_exec = helpers.redir_exec
 local source = helpers.source
 
 before_each(clear)
 
-describe(':let command', function()
+describe(':let', function()
   it('correctly lists variables with curly-braces', function()
     meths.set_var('v', {0})
     eq('\nv                     [0]', redir_exec('let {"v"}'))
@@ -42,4 +44,16 @@ describe(':let command', function()
       call feedkeys(":\e:echo l1 l3\n:echo 42\n:cq\n", "t")
     ]=])
   end)
+
+  it("sets environment variables", function()
+    local multibyte_multiline = [[\p* .ม .ม .ม .ม่ .ม่ .ม่ ֹ ֹ ֹ .ֹ .ֹ .ֹ ֹֻ ֹֻ ֹֻ
+                                  .ֹֻ .ֹֻ .ֹֻ ֹֻ ֹֻ ֹֻ .ֹֻ .ֹֻ .ֹֻ ֹ ֹ ֹ .ֹ .ֹ .ֹ ֹ ֹ ֹ .ֹ .ֹ .ֹ ֹֻ ֹֻ
+                                  .ֹֻ .ֹֻ .ֹֻ a a a ca ca ca à à à]]
+    command("let $NVIM_TEST1 = 'AìaB'")
+    command("let $NVIM_TEST2 = 'AaあB'")
+    command("let $NVIM_TEST3 = '"..multibyte_multiline.."'")
+    eq('AìaB', eval('$NVIM_TEST1'))
+    eq('AaあB', eval('$NVIM_TEST2'))
+    eq(multibyte_multiline, eval('$NVIM_TEST3'))
+  end)
 end)