diff --git a/server/setup-server.sh b/server/setup-server.sh
index f8618f4..13e66ff 100755
--- a/server/setup-server.sh
+++ b/server/setup-server.sh
@@ -43,6 +43,15 @@ else
   echo "==> Forge server already installed, skipping"
 fi
 
+# JVM heap flags go in user_jvm_args.txt, NOT on lazymc's command line — run.sh
+# forwards any args after "nogui" straight to Minecraft's own arg parser (not
+# the JVM), so passing -Xmx/-Xms there crashes with "X is not a recognized option".
+cat > "$SERVER_DIR/user_jvm_args.txt" <<EOF
+# Managed by setup-server.sh — edit MIN_RAM/MAX_RAM at the top of that script instead.
+-Xms${MIN_RAM}
+-Xmx${MAX_RAM}
+EOF
+
 # server.properties: lazymc will rewrite host/port/rcon itself, we just set gameplay-relevant bits
 touch "$SERVER_DIR/server.properties"
 for kv in "online-mode=false" "motd=LAN Party - Create & Delight" "difficulty=normal" "max-players=20"; do
@@ -73,7 +82,7 @@ fi
 cat > "$BASE_DIR/lazymc.toml" <<EOF
 [server]
 directory = "$SERVER_DIR"
-command = "bash run.sh nogui -Xms${MIN_RAM} -Xmx${MAX_RAM}"
+command = "bash run.sh nogui"
 address = "127.0.0.1:${MC_INTERNAL_PORT}"
 freeze_process = false
 wake_whitelist = false