diff --git a/src/ring/mock/request.clj b/src/ring/mock/request.clj
index 1d2eff8..c13b04a 100644
--- a/src/ring/mock/request.clj
+++ b/src/ring/mock/request.clj
@@ -4,8 +4,10 @@
             [clojure.string :as string]
             [ring.util.codec :as codec]
             [ring.util.mime-type :as mime])
-  (:import [java.io ByteArrayInputStream ByteArrayOutputStream File]
+  (:import [java.io ByteArrayInputStream ByteArrayOutputStream File InputStream]
+           [java.net URI]
            [java.nio.charset Charset]
+           [java.util Map]
            [org.apache.hc.core5.http ContentType HttpEntity]
            [org.apache.hc.client5.http.entity.mime MultipartEntityBuilder]))
 
@@ -75,9 +77,9 @@
 (defmethod body (class (byte-array 0)) [request bytes]
   (-> request
       (content-length (count bytes))
-      (assoc :body (java.io.ByteArrayInputStream. bytes))))
+      (assoc :body (ByteArrayInputStream. bytes))))
 
-(defmethod body java.util.Map [request params]
+(defmethod body Map [request params]
   (-> request
       (content-type "application/x-www-form-urlencoded")
       (body (encode-params params))))
@@ -99,11 +101,30 @@
 (defn- file? [f]
   (instance? File f))
 
-(defn- add-multipart-part [builder k v]
+(defn- str->bytes ^bytes [^String s]
+  (.getBytes s ^Charset default-charset))
+
+(defn- add-binary-body
+  [^MultipartEntityBuilder builder key value ^ContentType mimetype
+   ^String filename]
+  (let [k (name key)]
+    (cond
+      (string? value)
+      (.addBinaryBody builder k (str->bytes value) mimetype filename)
+      (bytes? value)
+      (.addBinaryBody builder k ^bytes value mimetype filename)
+      (file? value)
+      (.addBinaryBody builder k ^File value mimetype filename)
+      (instance? InputStream value)
+      (.addBinaryBody builder k ^InputStream value mimetype filename)
+      :else
+      (throw (IllegalArgumentException.
+               (str "Cannot encode a value of type " (type value)
+                    " as a multipart body."))))))
+
+(defn- add-multipart-part [^MultipartEntityBuilder builder k v]
   (let [param    (if (map? v) v {:value v})
-        value    (if (string? (:value param))
-                   (.getBytes (:value param) default-charset)
-                   (:value param))
+        value    (if (map? v) (:value v) v)
         mimetype (ContentType/parse
                   (or (:content-type param)
                       (when (file? value)
@@ -113,11 +134,11 @@
                         "application/octet-stream")))
         filename (or (:filename param)
                      (when (file? value) (.getName ^File value)))]
-    (.addBinaryBody builder (name k) value mimetype filename)))
+    (add-binary-body builder (name k) value mimetype filename)))
 
 (defn- multipart-entity ^HttpEntity [params]
   (let [builder (MultipartEntityBuilder/create)]
-    (.setCharset builder default-charset)
+    (.setCharset builder ^Charset default-charset)
     (doseq [[k v] params]
       (add-multipart-part builder k v))
     (.build builder)))
@@ -157,7 +178,7 @@
   ([method uri]
      (request method uri nil))
   ([method uri params]
-     (let [uri    (java.net.URI. uri)
+     (let [uri    (URI. uri)
            scheme (keyword (or (.getScheme uri) "http"))
            host   (or (.getHost uri) "localhost")
            port   (when (not= (.getPort uri) -1) (.getPort uri))
diff --git a/test/ring/mock/request_test.clj b/test/ring/mock/request_test.clj
index 5f0ca15..d9e781b 100644
--- a/test/ring/mock/request_test.clj
+++ b/test/ring/mock/request_test.clj
@@ -1,9 +1,11 @@
 (ns ring.mock.request-test
   (:require [clojure.java.io :as io]
+            [clojure.spec.alpha :as s]
             [clojure.test :refer [deftest is testing]]
             [ring.mock.request :refer [body content-length content-type cookie
                                        header json-body multipart-body
-                                       query-string request]]))
+                                       query-string request]])
+  (:import [java.io InputStream]))
 
 (deftest test-request
   (testing "relative uri"
@@ -130,19 +132,19 @@
 (deftest test-body
   (testing "string body"
     (let [resp (body {} "Hello World")]
-      (is (instance? java.io.InputStream (:body resp)))
+      (is (instance? InputStream (:body resp)))
       (is (= (slurp (:body resp)) "Hello World"))
       (is (= (:content-length resp) 11))))
   (testing "map body"
     (let [resp (body {} (array-map :foo "bar" :fi ["fi" "fo" "fum"]))]
-      (is (instance? java.io.InputStream (:body resp)))
+      (is (instance? InputStream (:body resp)))
       (is (= (slurp (:body resp)) "foo=bar&fi=fi&fi=fo&fi=fum"))
       (is (= (:content-length resp) 26))
       (is (= (:content-type resp)
              "application/x-www-form-urlencoded"))))
   (testing "bytes body"
     (let [resp (body {} (.getBytes "foo"))]
-      (is (instance? java.io.InputStream (:body resp)))
+      (is (instance? InputStream (:body resp)))
       (is (= (slurp (:body resp)) "foo"))
       (is (= (:content-length resp) 3)))))
 
@@ -150,7 +152,7 @@
   (testing "json body"
     (let [resp (json-body {} {:baz ["qu" "qi" "qo"]})]
       (is (= (:content-type resp) "application/json"))
-      (is (instance? java.io.InputStream (:body resp)))
+      (is (instance? InputStream (:body resp)))
       (is (= (slurp (:body resp))
              "{\"baz\":[\"qu\",\"qi\",\"qo\"]}"))
       (is (= (:content-length resp) 24)))))
@@ -229,7 +231,16 @@
                   "filename=\"test.html\"\r\n"
                   "Content-Type: text/html\r\n\r\n"
                   "a\n\r\n"
-                  "--" boundary "--\r\n"))))))
+                  "--" boundary "--\r\n")))))
+  (testing "not supported type"
+    (try
+      (multipart-body {} {:foo :keyword
+                          :bar {:value        :keyword
+                                :content-type "text/html"
+                                :filename     "test.html"}})
+      (catch Exception e
+        (let [expected-message "Cannot encode a value of type class clojure.lang.Keyword as a multipart body."]
+          (is (= expected-message (.getMessage ^Exception e))))))))
 
 (defmacro when-clojure-spec
   [& body]