Probably not the best fix. Seems to work. Includes a few tests.

-Dale

diff --git a/module/web/uri.scm b/module/web/uri.scm
index 8e0b9bee7..d6758fcc6 100644
--- a/module/web/uri.scm
+++ b/module/web/uri.scm
@@ -212,7 +212,9 @@ for ‘build-uri’ except there is no scheme."
 (and (regexp-exec domain-label-regexp
 (substring host start end))
 (lp (1+ end)))
- (regexp-exec top-label-regexp host start)))))))
+ (if (< start (string-length host))
+ (regexp-exec top-label-regexp host start)
+ #t)))))))

 (define userinfo-pat
 (string-append "[" letters digits "_.!~*'();:&=+$,-]+"))
diff --git a/test-suite/tests/web-uri.test
b/test-suite/tests/web-uri.test
index 95fd82f16..c49142d48 100644
--- a/test-suite/tests/web-uri.test
+++ b/test-suite/tests/web-uri.test
@@ -367,6 +367,9 @@
 (pass-if "//bad.host.1"
 (not (string->uri-reference "//bad.host.1")))

+ (pass-if "//bad.host.."
+ (not (string->uri-reference "//bad.host..")))
+
 (pass-if "http://1.good.host"
 (uri=? (string->uri-reference "http://1.good.host")
 #:scheme 'http #:host "1.good.host" #:path ""))
@@ -375,6 +378,10 @@
 (uri=? (string->uri-reference "//1.good.host")
 #:host "1.good.host" #:path ""))

+ (pass-if "//1.good.host."
+ (uri=? (string->uri-reference "//1.good.host.")
+ #:host "1.good.host." #:path ""))
+
 (when (memq 'socket *features*)
 (pass-if "http://192.0.2.1"
 (uri=? (string->uri-reference "http://192.0.2.1")