diff --git a/src/amduatd.c b/src/amduatd.c
index 86639bb..f081890 100644
--- a/src/amduatd.c
+++ b/src/amduatd.c
@@ -280,6 +280,7 @@ static const char k_amduatd_ui_html[] =
     "\n"
     "    async function ensureConcept(name){\n"
     "      const resp = await fetch('/v1/concepts',{method:'POST',headers:{'Content-Type':'application/json'},body:JSON.stringify({name})});\n"
+    "      if(resp.status === 409) return; // already exists\n"
     "      if(!resp.ok) throw new Error(await resp.text());\n"
     "    }\n"
     "\n"