diff --git a/lib/sinatra/base.rb b/lib/sinatra/base.rb
index aef747e794..17e7175f95 100644
--- a/lib/sinatra/base.rb
+++ b/lib/sinatra/base.rb
@@ -1089,7 +1089,14 @@ def invoke
 
     # Dispatch a request with error handling.
     def dispatch!
-      @params.merge!(@request.params).each { |key, val| @params[key] = val && force_encoding(val.dup) }
+      @params.merge!(@request.params).each do |key, val|
+        @params[key] =
+          begin
+            force_encoding(val.dup)
+          rescue TypeError
+            val
+          end
+      end
 
       invoke do
         static! if settings.static? && (request.get? || request.head?)
diff --git a/test/middleware_test.rb b/test/middleware_test.rb
index 7f71588696..370f874a8b 100644
--- a/test/middleware_test.rb
+++ b/test/middleware_test.rb
@@ -78,4 +78,23 @@ def call(env)
     @app.use FreezeMiddleware
     get '/Foo'
   end
+
+  class SpecialConstsMiddleware < MockMiddleware
+    def call(env)
+      req = Rack::Request.new(env)
+      req.update_param('s', :s)
+      req.update_param('i', 1)
+      req.update_param('c', 3.to_c)
+      req.update_param('t', true)
+      req.update_param('f', false)
+      req.update_param('n', nil)
+      super
+    end
+  end
+
+  it "handles params when the params contains true/false values" do
+    @app.use SpecialConstsMiddleware
+    get '/'
+  end
+
 end