diff --git a/src/integrations.py b/src/integrations.py
index 3cb53a415..aa6c4982e 100644
--- a/src/integrations.py
+++ b/src/integrations.py
@@ -216,7 +216,14 @@ def _normalize_integration_base_url(base_url: Any) -> str:
 
 
 def _join_integration_url(base_url: str, path: str) -> str:
-    return urljoin(base_url.rstrip("/") + "/", path.lstrip("/"))
+    base = base_url.rstrip("/")
+    rel = path.lstrip("/")
+    if not rel:
+        # A bare "/" must resolve to the base URL itself, not base + "/".
+        # POST-to-base integrations (e.g. Discord webhooks) 404 on the
+        # trailing-slash variant of their URL.
+        return base
+    return urljoin(base + "/", rel)
 
 
 def load_integrations() -> List[Dict[str, Any]]:
diff --git a/tests/test_integrations_url_join.py b/tests/test_integrations_url_join.py
new file mode 100644
index 000000000..a5e19722e
--- /dev/null
+++ b/tests/test_integrations_url_join.py
@@ -0,0 +1,116 @@
+"""Tests for integration URL construction in execute_api_call.
+
+Covers the trailing-slash regression from #5138: a bare "/" path must
+resolve to the base URL itself, not base + "/". Discord webhook URLs
+404 on the trailing-slash variant, so api_call against a
+POST-to-base integration silently failed.
+"""
+import sys
+import types
+from unittest.mock import AsyncMock, MagicMock, patch
+
+import pytest
+
+# ---------------------------------------------------------------------------
+# Minimal stubs so src.integrations can be imported without heavy deps
+# ---------------------------------------------------------------------------
+
+for mod_name in ("core", "core.atomic_io", "core.platform_compat"):
+    if mod_name not in sys.modules:
+        sys.modules[mod_name] = types.ModuleType(mod_name)
+
+core_atomic = sys.modules["core.atomic_io"]
+if not hasattr(core_atomic, "atomic_write_json"):
+    core_atomic.atomic_write_json = lambda *a, **kw: None  # type: ignore
+
+core_compat = sys.modules["core.platform_compat"]
+if not hasattr(core_compat, "safe_chmod"):
+    core_compat.safe_chmod = lambda *a, **kw: None  # type: ignore
+
+if "src.secret_storage" not in sys.modules:
+    stub = types.ModuleType("src.secret_storage")
+    stub.encrypt = lambda s: s  # type: ignore
+    stub.decrypt = lambda s: s  # type: ignore
+    stub.is_encrypted = lambda s: False  # type: ignore
+    sys.modules["src.secret_storage"] = stub
+
+if "src.constants" not in sys.modules:
+    stub_c = types.ModuleType("src.constants")
+    stub_c.DATA_DIR = "/tmp"  # type: ignore
+    stub_c.INTEGRATIONS_FILE = "/tmp/integrations_test.json"  # type: ignore
+    stub_c.SETTINGS_FILE = "/tmp/settings_test.json"  # type: ignore
+    sys.modules["src.constants"] = stub_c
+
+from src import integrations  # noqa: E402
+
+
+# ---------------------------------------------------------------------------
+# _join_integration_url unit tests
+# ---------------------------------------------------------------------------
+
+WEBHOOK_BASE = "https://discord.com/api/webhooks/123/tokentokentoken"
+
+
+@pytest.mark.parametrize(
+    "base,path,expected",
+    [
+        # Bare "/" (the minimum path execute_api_call accepts) must not
+        # grow a trailing slash — Discord webhooks 404 on it (#5138).
+        (WEBHOOK_BASE, "/", WEBHOOK_BASE),
+        (WEBHOOK_BASE + "/", "/", WEBHOOK_BASE),
+        (WEBHOOK_BASE, "", WEBHOOK_BASE),
+        # Normal paths keep joining exactly as before.
+        ("http://api.example.com", "/items", "http://api.example.com/items"),
+        ("http://api.example.com/", "/items", "http://api.example.com/items"),
+        ("http://host/base", "/v1/me", "http://host/base/v1/me"),
+        # A deliberate trailing slash inside a non-empty path is preserved
+        # (e.g. linkding's /api/tags/, Home Assistant's /api/).
+        ("http://host", "/api/tags/", "http://host/api/tags/"),
+        ("http://host", "/api/", "http://host/api/"),
+    ],
+)
+def test_join_integration_url(base, path, expected):
+    assert integrations._join_integration_url(base, path) == expected
+
+
+# ---------------------------------------------------------------------------
+# Behavioral test through execute_api_call
+# ---------------------------------------------------------------------------
+
+DISCORD_INTEGRATION = {
+    "id": "discord_test",
+    "name": "Discord Webhook",
+    "enabled": True,
+    "base_url": WEBHOOK_BASE,
+    "auth_type": "none",
+    "api_key": "",
+    "auth_header": "",
+    "auth_param": "",
+    "description": "",
+    "preset": "discord_webhook",
+}
+
+
+@pytest.mark.asyncio
+async def test_api_call_root_path_has_no_trailing_slash():
+    mock_resp = MagicMock()
+    mock_resp.status_code = 204
+    mock_resp.headers = {"content-type": "text/plain"}
+    mock_resp.text = ""
+
+    mock_client = AsyncMock()
+    mock_client.__aenter__ = AsyncMock(return_value=mock_client)
+    mock_client.__aexit__ = AsyncMock(return_value=None)
+    mock_client.request = AsyncMock(return_value=mock_resp)
+
+    with (
+        patch.object(integrations, "_find_integration", return_value=DISCORD_INTEGRATION),
+        patch("httpx.AsyncClient", return_value=mock_client),
+    ):
+        result = await integrations.execute_api_call(
+            "discord_test", "POST", "/", body={"content": "test"}
+        )
+
+    assert result.get("exit_code") == 0
+    requested_url = mock_client.request.call_args.args[1]
+    assert requested_url == WEBHOOK_BASE