diff --git a/scripts/jellyfin-providers.sh b/scripts/jellyfin-providers.sh
index c982b65..9436e9d 100755
--- a/scripts/jellyfin-providers.sh
+++ b/scripts/jellyfin-providers.sh
@@ -135,7 +135,18 @@ text = escape(val)
 if pat.search(src):
     out = pat.sub(lambda m: f"{m.group(1)}<{elem}>{text}</{elem}>", src, count=1)
 else:
-    out = src.replace("</Configuration>", f"  <{elem}>{text}</{elem}>\n</Configuration>", 1)
+    # The plugin owns this file and writes it under ITS OWN root element
+    # (TheTVDB's is <PluginConfiguration>), and its serializer omits a
+    # null-valued setting entirely — so the element being filled can be
+    # absent outright, and a hardcoded </Configuration> anchor then matches
+    # nothing. Anchor on the document's real root instead.
+    out = src
+    root = re.search(r"<([A-Za-z_][\w.:-]*)[^>]*>", src)
+    if root and ("</%s>" % root.group(1)) in src:
+        name = root.group(1)
+        out = src.replace(
+            "</%s>" % name, f"  <{elem}>{text}</{elem}>\n</{name}>", 1
+        )
 if out == src:
     raise SystemExit(f"{xml_path}: no place to write <{elem}>")
 
diff --git a/tests/jellyfin_providers.bats b/tests/jellyfin_providers.bats
index c9e71d0..416da6e 100755
--- a/tests/jellyfin_providers.bats
+++ b/tests/jellyfin_providers.bats
@@ -13,9 +13,12 @@
 #   3. a downloaded plugin artifact is accepted only on its pinned sha256, its
 #      official guid and its pinned version (a swapped or downgraded artifact
 #      is refused before anything lands in plugins/);
-#   4. the TMDb key is written into the EXISTING config with every other
-#      setting preserved — Jellyfin owns that file, and clobbering it would
-#      silently reset country, language and adult settings;
+#   4. a key is written into the EXISTING config with every other setting
+#      preserved, under whatever root that file's owner chose — Jellyfin's core
+#      configs say `<Configuration>`, TheTVDB writes `<PluginConfiguration>` and
+#      omits a null setting outright, so the element to fill can be absent and
+#      the anchor has to come from the file; clobbering the file would silently
+#      reset country, language and adult settings;
 #   5. a TVDB config the operator already saved through the UI is kept;
 #   6. install is idempotent: a second run changes no byte;
 #   7. whatever is replaced is copied to the trash first (fleet law: never
@@ -254,6 +257,38 @@ XML
     grep -qF '<EnableSeasonPathMatching>true</EnableSeasonPathMatching>' "$cfg"
 }
 
+@test "the key lands in a plugin-written config with no ApiKey element" {
+    # What TheTVDB actually writes on a fresh install: its own root element and
+    # no <ApiKey /> at all, because its serializer drops null settings. The
+    # installer used to anchor on </Configuration> and refuse this file.
+    cat >"$JF/plugins/configurations/Jellyfin.Plugin.Tvdb.xml" <<XML
+<?xml version="1.0" encoding="utf-8"?>
+<PluginConfiguration xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
+  <SubscriberPIN />
+  <CacheDurationInHours>1</CacheDurationInHours>
+  <OriginalTitle>true</OriginalTitle>
+</PluginConfiguration>
+XML
+    run prov install
+    [ "$status" -eq 0 ]
+    printf '%s\n' "${lines[@]}" | grep -qiF 'filled the ApiKey'
+    local cfg="$JF/plugins/configurations/Jellyfin.Plugin.Tvdb.xml"
+    grep -qF "<ApiKey>$TVDB_KEY</ApiKey>" "$cfg"
+    grep -qF '<CacheDurationInHours>1</CacheDurationInHours>' "$cfg"
+    grep -qF '<OriginalTitle>true</OriginalTitle>' "$cfg"
+}
+
+@test "a config file with no root element is refused by name" {
+    # The guard still has to fire when there is genuinely nowhere to write —
+    # a refusal naming the file beats inventing a document shape.
+    printf '<?xml version="1.0" encoding="utf-8"?>\n' \
+        >"$JF/plugins/configurations/Jellyfin.Plugin.Tvdb.xml"
+    run prov install
+    [ "$status" -ne 0 ]
+    printf '%s\n' "${lines[@]}" | grep -qF 'Jellyfin.Plugin.Tvdb.xml'
+    printf '%s\n' "${lines[@]}" | grep -qiF 'no place to write'
+}
+
 @test "a pin in the TVDB secret lands in the plugin config" {
     # A subscriber-shaped key needs the account's PIN beside it; a licensed key
     # does not, so the element appears only when the secret carries one.