diff --git a/postgrest/base_client.py b/postgrest/base_client.py
index 575080d..db6fffc 100644
--- a/postgrest/base_client.py
+++ b/postgrest/base_client.py
@@ -5,7 +5,7 @@
 
 from httpx import BasicAuth, Timeout
 
-from .utils import AsyncClient, SyncClient
+from .utils import AsyncClient, SyncClient, is_http_url
 
 
 class BasePostgrestClient(ABC):
@@ -21,6 +21,8 @@ def __init__(
         verify: bool = True,
         proxy: Optional[str] = None,
     ) -> None:
+        if not is_http_url(base_url):
+            ValueError("base_url must be a valid HTTP URL string")
         headers = {
             **headers,
             "Accept-Profile": schema,
diff --git a/postgrest/utils.py b/postgrest/utils.py
index 39dc1e2..31cda49 100644
--- a/postgrest/utils.py
+++ b/postgrest/utils.py
@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 from typing import Any, Type, TypeVar, cast, get_origin
+from urllib.parse import urlparse
 
 from httpx import AsyncClient  # noqa: F401
 from httpx import Client as BaseClient  # noqa: F401
@@ -35,3 +36,7 @@ def get_origin_and_cast(typ: type[type[_T]]) -> type[_T]:
     # See: definitions of request builders that use multiple-inheritance
     # like AsyncFilterRequestBuilder
     return cast(Type[_T], get_origin(typ))
+
+
+def is_http_url(url: str) -> bool:
+    return urlparse(url).scheme in {"https", "http"}