diff --git a/R/zzz.R b/R/zzz.R
index a7b4c41d..b15e3326 100644
--- a/R/zzz.R
+++ b/R/zzz.R
@@ -5,22 +5,36 @@
   ## it's in "/usr/share/zoneinfo" where CCTZ looks by default. On some systems
   ## (solaris, osx) it might be in a different location. So, help ourselves by
   ## setting the TZDIR env var, but only if it's not already set.
-  if (Sys.getenv("TZDIR") == "") {
-    ## adapted from OlsonNames function
-    tzdir <-
-      if (.Platform$OS.type == "windows") {
-        file.path(R.home("share"), "zoneinfo")
-      } else if (!file.exists("/usr/share/zoneinfo")) {
-        tzdirs <- c(file.path(R.home("share"), "zoneinfo"),
-                    "/usr/share/lib/zoneinfo", "/usr/lib/zoneinfo",
-                    "/usr/local/etc/zoneinfo", "/etc/zoneinfo",
-                    "/usr/etc/zoneinfo")
-        tzdirs <- tzdirs[file.exists(tzdirs)]
-        if (length(tzdirs)) tzdirs[[1]]
-        else NULL
-      }
-    if (!is.null(tzdir)) {
-      Sys.setenv(TZDIR = tzdir)
+
+  ## adapted from Syz.timezone and OlsonNames function
+  .find_tzdir <- function() {
+    if (.Platform$OS.type == "windows")
+      return(file.path(R.home("share"), "zoneinfo"))
+    tzdirs <- c("/usr/share/zoneinfo",
+                "/usr/share/lib/zoneinfo",
+                "/usr/lib/zoneinfo",
+                "/usr/local/etc/zoneinfo",
+                "/etc/zoneinfo",
+                "/usr/etc/zoneinfo",
+                "/usr/share/zoneinfo.default",
+                "/var/db/timezone/zoneinfo",
+                file.path(R.home("share"), "zoneinfo"))
+    tzdirs <- tzdirs[file.exists(tzdirs)]
+    if (length(tzdirs)) tzdirs[[1]]
+    else NULL
+  }
+
+  tzdir <- Sys.getenv("TZDIR")
+  if (tzdir == "internal") {
+    Sys.setenv(TZDIR = file.path(R.home("share"), "zoneinfo"))
+  } else if (tzdir == "macOS") {
+    if (!is.null(dir <- .find_tzdir()))
+      Sys.setenv(TZDIR = dir)
+  } else if (tzdir == "") {
+    # not checking for /usr/share/zoneinfo which is the default in CCTZ
+    if (!file.exists("/usr/share/zoneinfo")) {
+      if (!is.null(dir <- .find_tzdir()))
+        Sys.setenv(TZDIR = dir)
     }
   }