diff --git a/src/gemini/gemini-parser.lisp b/src/gemini/gemini-parser.lisp
index 2fba60d..f569f1a 100644
--- a/src/gemini/gemini-parser.lisp
+++ b/src/gemini/gemini-parser.lisp
@@ -247,8 +247,11 @@
          (actual-port (if port
                           (to-s port)
                           (to-s +gemini-default-port+)))
+         (actual-host (if (iri:ipv6-address-p host)
+                          (strcat "[" host "]")
+                          host))
          (iri (strcat scheme         "://"
-                      host            ":"
+                      actual-host    ":"
                       actual-port     "/"
                       actual-path)))
     (when query
diff --git a/src/iri-parser.lisp b/src/iri-parser.lisp
index b2d3bd7..db5f0cf 100644
--- a/src/iri-parser.lisp
+++ b/src/iri-parser.lisp
@@ -335,3 +335,15 @@
 (defun absolute-url-p (url)
   (when-let ((iri (iri:iri-parse url :null-on-error t)))
     (not (null (uri:scheme iri)))))
+
+(defun ipv4-address-p (string)
+  (ignore-errors
+   (let ((bytes (mapcar #'parse-integer
+                        (cl-ppcre:split "\\."
+                                        string))))
+     (and (= (length bytes)
+             4)
+          (every (lambda (a) (<= 0 a 255)) bytes)))))
+
+(defun ipv6-address-p (string)
+  (cl-ppcre:scan ":" string))
diff --git a/src/package.lisp b/src/package.lisp
index 5d3a99b..e6ed1f5 100644
--- a/src/package.lisp
+++ b/src/package.lisp
@@ -676,7 +676,9 @@
    :render-iri
    :make-iri
    :iri-parse
-   :absolute-url-p))
+   :absolute-url-p
+   :ipv4-address-p
+   :ipv6-address-p))
 
 (defpackage :x509
   (:use