diff --git a/heroics.gemspec b/heroics.gemspec
index 469d782..66ae460 100644
--- a/heroics.gemspec
+++ b/heroics.gemspec
@@ -31,6 +31,5 @@ Gem::Specification.new do |spec|
   spec.add_dependency 'excon'
   spec.add_dependency 'multi_json', '>= 1.9.2'
   spec.add_dependency 'moneta'
-  spec.add_dependency 'webrick'
   spec.add_dependency 'base64'
 end
diff --git a/lib/heroics.rb b/lib/heroics.rb
index e9a4ac5..81845d6 100644
--- a/lib/heroics.rb
+++ b/lib/heroics.rb
@@ -4,7 +4,6 @@
 require 'excon'
 require 'multi_json'
 require 'uri'
-require 'webrick'
 require 'zlib'
 
 # Heroics is an HTTP client for an API described by a JSON schema.
diff --git a/lib/heroics/schema.rb b/lib/heroics/schema.rb
index 891f360..a23dd1c 100644
--- a/lib/heroics/schema.rb
+++ b/lib/heroics/schema.rb
@@ -334,7 +334,39 @@ def lookup_parameter(path, schema)
     # @return [String] The formatted parameter.
     def format_parameter(parameter)
       formatted_parameter = parameter.instance_of?(Time) ? iso_format(parameter) : parameter.to_s
-      WEBrick::HTTPUtils.escape formatted_parameter
+      url_escape_parameter formatted_parameter
+    end
+
+    # URL escape a path parameter. Copied from WEBrick::HTTPUtils.escape:
+    # https://github.com/ruby/webrick/blob/master/lib/webrick/httputils.rb#L498
+    #
+    # @param [Fixnum,String,TrueClass,FalseClass,Time] The parameter to escape.
+    # @return [String] The escaped parameter.
+    def url_escape_parameter(parameter)
+      # Note: this RegEx is obtained by executing WEBrick::HTTPUtils::UNESCAPED,
+      # splitting it over multiple lines and using the x modifier to make this possible.
+      regex = %r{
+        ([
+          \x00\x01\x02\x03\x04\x05\x06\x07\x08
+          \t\n\v\f\r
+          \x0E\x0F\x10\x11\x12\x13\x14\x15\x16
+          \x17\x18\x19\x1A\x1B\x1C\x1D\x1E\x1F\x7F
+          \ <>\#%"\{\}\|\\\^\[\]`
+          \x80\x81\x82\x83\x84\x85\x86\x87\x88\x89\x8A\x8B\x8C\x8D\x8E\x8F
+          \x90\x91\x92\x93\x94\x95\x96\x97\x98\x99\x9A\x9B\x9C\x9D\x9E\x9F
+          \xA0\xA1\xA2\xA3\xA4\xA5\xA6\xA7\xA8\xA9\xAA\xAB\xAC\xAD\xAE\xAF
+          \xB0\xB1\xB2\xB3\xB4\xB5\xB6\xB7\xB8\xB9\xBA\xBB\xBC\xBD\xBE\xBF
+          \xC0\xC1\xC2\xC3\xC4\xC5\xC6\xC7\xC8\xC9\xCA\xCB\xCC\xCD\xCE\xCF
+          \xD0\xD1\xD2\xD3\xD4\xD5\xD6\xD7\xD8\xD9\xDA\xDB\xDC\xDD\xDE\xDF
+          \xE0\xE1\xE2\xE3\xE4\xE5\xE6\xE7\xE8\xE9\xEA\xEB\xEC\xED\xEE\xEF
+          \xF0\xF1\xF2\xF3\xF4\xF5\xF6\xF7\xF8\xF9\xFA\xFB\xFC\xFD\xFE\xFF
+        ])
+      }nx
+
+      parameter = parameter.b
+      parameter.gsub!(regex) {"%%%02X" % $1.ord}
+      # %-escaped string should contain US-ASCII only
+      parameter.force_encoding(Encoding::US_ASCII)
     end
 
     # Convert a time to an ISO 8601 combined data and time format.