diff -r 66bde992ebd0 -r a5f3e1e5e744 src/server/test/io.c
--- a/src/server/test/io.c	Mon Mar 16 19:44:18 2026 +0100
+++ b/src/server/test/io.c	Tue Mar 17 20:49:37 2026 +0100
@@ -675,6 +675,41 @@
     }
 }
 
+CX_TEST(test_io_httpstream_chunked_write_partial_writev) {
+    Session *sn = testutil_session();
+    
+    TestIOStream *st = testutil_iostream(2048, TRUE);
+    IOStream *http = httpstream_new(sn->pool, (IOStream*)st);
+    httpstream_enable_chunked_write(http);
+    io_set_max_writes(1);
+    
+    CX_TEST_DO {
+    
+        memset(st->buf->space, 0, st->buf->capacity);
+
+        char *msg = "hello world!";
+        size_t msglen = strlen(msg);
+
+        // Test: write complete chunk header, zero data
+
+        st->max_write = 3;
+        ssize_t w = net_write(http, msg, msglen);
+        
+        CX_TEST_ASSERT(w == 0);
+        
+        st->max_write = 1000;
+        w = net_write(http, msg, msglen);
+        
+        CX_TEST_ASSERT(w == msglen);
+        
+        CX_TEST_ASSERT(!memcmp(st->buf->space, "c\r\nhello world!\r\n", st->buf->size));
+
+        testutil_destroy_session(sn);
+        testutil_iostream_destroy(st);
+    
+    }
+}
+
 CX_TEST(test_io_httpstream_chunked_write_data_2x) {
     Session *sn = testutil_session();