We find an asymptotic formula for the number of primitive vectors (z 1 , . . . , z 4 ) ∈ (Z =0 ) 4 such that z 1 , . . . , z 4 are all squareful and bounded by B, andOur result agrees in the power of B and log B with the Campana-Manin conjecture of Pieropan, Smeets, Tanimoto and Várilly-Alvarado. Contents 1. Introduction 1 2. The Campana-Manin conjecture 5 3. Dealing with the large coefficients 10 4. The circle method 14 5. Proof of Theorem 1.1 36 References 43