[Haskell-beginners] Non-exhaustive patterns in function error

[Galaxy Being]

I have this

intersect1 :: ([a],[a]) -> [a]
intersect1 (s,[])              = []
interesct1 (s,t:ts) | elem t s = t : intersect1 (s,ts)
                    | otherwise = intersect1 (s,ts)

and when I try this

intersect1 ([1,2],[1,2,3])

I get the error

 Non-exhaustive patterns in function intersect1

Not sure what's wrong with this.

LB
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