diff --git a/src/libmain/shared.cc b/src/libmain/shared.cc
index a6e8f352a..f91558f50 100644
--- a/src/libmain/shared.cc
+++ b/src/libmain/shared.cc
@@ -162,6 +162,14 @@ void initNix()
 
     if (char *pack = getenv("_NIX_OPTIONS"))
         settings.unpack(pack);
+
+    /* On macOS, don't use the per-session TMPDIR (as set e.g. by
+       sshd). This breaks build users because they don't have access
+       to the TMPDIR, in particular in ‘nix-store --serve’. */
+#if __APPLE__
+    if (getuid() == 0 && hasPrefix(getEnv("TMPDIR"), "/var/folders/"))
+        unsetenv("TMPDIR");
+#endif
 }