diff --git a/lib/webrick/httputils.rb b/lib/webrick/httputils.rb
index e2c2a40..1d9324f 100644
--- a/lib/webrick/httputils.rb
+++ b/lib/webrick/httputils.rb
@@ -471,14 +471,20 @@ def parse_form_data(io, boundary)
 
     def _make_regex(str) /([#{Regexp.escape(str)}])/n end
     def _make_regex!(str) /([^#{Regexp.escape(str)}])/n end
+    def _ensure_string(str)
+      unless str.is_a?(String)
+        raise TypeError, "no implicit conversion of #{str.class} into String"
+      end
+      str
+    end
     def _escape(str, regex)
-      str = str.b
+      str = _ensure_string(str).b
       str.gsub!(regex) {"%%%02X" % $1.ord}
       # %-escaped string should contain US-ASCII only
       str.force_encoding(Encoding::US_ASCII)
     end
     def _unescape(str, regex)
-      str = str.b
+      str = _ensure_string(str).b
       str.gsub!(regex) {$1.hex.chr}
       # encoding of %-unescaped string is unknown
       str
@@ -519,7 +525,7 @@ def escape_form(str)
     # Unescapes form reserved characters in +str+
 
     def unescape_form(str)
-      _unescape(str.gsub(/\+/, " "), ESCAPED)
+      _unescape(_ensure_string(str).gsub(/\+/, " "), ESCAPED)
     end
 
     ##
diff --git a/test/webrick/test_httputils.rb b/test/webrick/test_httputils.rb
index 00f297b..86d9a99 100644
--- a/test/webrick/test_httputils.rb
+++ b/test/webrick/test_httputils.rb
@@ -98,4 +98,14 @@ def test_escape_path
     assert_equal("/foo/bar/", escape_path("/foo/bar/"))
     assert_equal("/%25foo/bar/", escape_path("/%foo/bar/"))
   end
+
+  def test_escape_with_nil_raises_clear_type_error
+    # [Bug: nil raised a confusing NoMethodError ("undefined method 'b'
+    # for nil:NilClass") instead of a clear, documented error - see
+    # https://github.com/ruby/webrick/issues/96
+    [:escape, :unescape, :escape_form, :unescape_form].each do |meth|
+      err = assert_raise(TypeError) { send(meth, nil) }
+      assert_equal("no implicit conversion of NilClass into String", err.message)
+    end
+  end
 end