diff --git a/src/ahttpx/_request.py b/src/ahttpx/_request.py
index 78b82282d0..a247b8b458 100644
--- a/src/ahttpx/_request.py
+++ b/src/ahttpx/_request.py
@@ -29,6 +29,11 @@ def __init__(
         if "Host" not in self.headers:
             self.headers = self.headers.copy_set("Host", self.url.netloc)
 
+        if self.url.scheme not in ('http', 'https'):
+            raise ValueError(f'Invalid scheme for URL {str(self.url)!r}.')
+        if not self.url.netloc:
+            raise ValueError(f'Missing host for URL {str(self.url)!r}.')
+
         if content is not None:
             if isinstance(content, bytes):
                 self.stream = ByteStream(content)
diff --git a/src/httpx/_request.py b/src/httpx/_request.py
index 1b739b1872..03c78dfea2 100644
--- a/src/httpx/_request.py
+++ b/src/httpx/_request.py
@@ -28,6 +28,11 @@ def __init__(
         # A client MUST include a Host header field in all HTTP/1.1 request messages.
         if "Host" not in self.headers:
             self.headers = self.headers.copy_set("Host", self.url.netloc)
+        
+        if self.url.scheme not in ('http', 'https'):
+            raise ValueError(f'Invalid scheme for URL {str(self.url)!r}.')
+        if not self.url.netloc:
+            raise ValueError(f'Missing host for URL {str(self.url)!r}.')
 
         if content is not None:
             if isinstance(content, bytes):
diff --git a/tests/test_request.py b/tests/test_request.py
index a69e1d1358..cab0a5e109 100644
--- a/tests/test_request.py
+++ b/tests/test_request.py
@@ -1,4 +1,5 @@
 import httpx
+import pytest
 
 
 class ByteIterator:
@@ -77,3 +78,13 @@ def test_request_empty_post():
         "Content-Length": "0",
     }
     assert r.read() == b''
+
+
+def test_request_invalid_scheme():
+    with pytest.raises(ValueError):
+        httpx.Request("GET", "ws://example.com")
+
+
+def test_request_missing_host():
+    with pytest.raises(ValueError):
+        r = httpx.Request("GET", "https:/example.com")