diff --git a/nix/microvm/base.nix b/nix/microvm/base.nix
index d40027f4..da3b56da 100644
--- a/nix/microvm/base.nix
+++ b/nix/microvm/base.nix
@@ -307,6 +307,13 @@ in {
     options = ["bind"];
     depends = ["/persist"];
   };
+  # bind mount /tmp so our tmp is disk backed...
+  fileSystems."/tmp" = {
+    device = "/persist/tmp";
+    fsType = "none";
+    options = ["bind"];
+    depends = ["/persist"];
+  };
 
   # create bind sources before local-fs.target, which means we have to do this
   # at initrd time
@@ -323,5 +330,8 @@ in {
     "/sysroot/persist/var".d = {
       mode = "0755";
     };
+    "/sysroot/persist/tmp".d = {
+      mode = "1777";
+    };
   };
 }
diff --git a/spindle/engines/microvm/test-spindle-microvm.sh b/spindle/engines/microvm/test-spindle-microvm.sh
index 6385ec69..697bcc9f 100755
--- a/spindle/engines/microvm/test-spindle-microvm.sh
+++ b/spindle/engines/microvm/test-spindle-microvm.sh
@@ -500,10 +500,16 @@ case "$http_version" in
         ;;
 esac
 
+if [ "$(stat -c %d /tmp)" = "$(stat -c %d /workspace)" ]; then
+    echo "tmp_on_persist=yes"
+else
+    echo "tmp_on_persist=no"
+fi
+
 /run/current-system/sw/bin/nix-store --realise "$store_path" >/dev/null
 ' bash "$test_store_path") || return 1
 
-    check_needles "$out" "^http_version=2(\\.0)?$" || return 1
+    check_needles "$out" "^http_version=2(\\.0)?$" "^tmp_on_persist=yes$" || return 1
     echo "success: store path realized from cache and cache proxy accepted cleartext HTTP/2"
 }