diff --git a/lisp/net/soap-client.el b/lisp/net/soap-client.el
index 7402464..bee3a12 100644
--- a/lisp/net/soap-client.el
+++ b/lisp/net/soap-client.el
@@ -536,9 +536,10 @@ soap-encode-xs-basic-type
                 (number-to-string value))
 
                (base64Binary
-                (unless (stringp value)
-                  (error "Not a string value for base64Binary"))
-                (base64-encode-string (encode-coding-string value 'utf-8)))
+                (unless (and (stringp value)
+                             (not (multibyte-string-p value)))
+                  (error "Not a unibyte string value for base64Binary"))
+                (base64-encode-string value))
 
                (otherwise
                 (error "Don't know how to encode %s for type %s"
@@ -682,7 +683,7 @@ soap-decode-xs-basic-type
                decimal byte float double duration)
          (string-to-number (car contents)))
         (boolean (string= (downcase (car contents)) "true"))
-        (base64Binary (decode-coding-string (base64-decode-string (car contents)) 'utf-8))
+        (base64Binary (base64-decode-string (car contents)))
         (anyType (soap-decode-any-type node))
         (Array (soap-decode-array node))))))
 
@@ -3096,7 +3097,9 @@ soap-invoke
 NOTE: The SOAP service provider should document the available
 operations and their parameters for the service.  You can also
 use the `soap-inspect' function to browse the available
-operations in a WSDL document."
+operations in a WSDL document.  `soap-invoke' base64-decodes
+base64Binary return values into unibyte strings; these
+byte-strings require further interpretation by the caller."
   (apply #'soap-invoke-internal nil nil wsdl service operation-name parameters))
 
 (defun soap-invoke-async (callback cbargs wsdl service operation-name