Poland's president has invited his compatriots to make suggestions for a new constitution to replace one that took effect 20 years ago.

President Andrzej Duda is calling on ordinary Poles to send their ideas to the Senate over the next year, with the aim of holding a referendum in November 2018 on what changes are needed.

Duda first floated the idea in May, apparently taking the governing party by surprise. It was seen as an effort to demonstrate his independence from ruling party leader Jaroslaw Kaczynski, Poland's most influential politician.

In a speech Friday in Gdansk, Duda said the existing constitution — which took effect seven years after democracy was restored in Poland — was "interim," had shortcomings and wasn't fit for a mature democracy.