Corrigendum to: Sectional monodromy groups of projective curves (Journal of the London Mathematical Society, (2021), 103, 1, (314-335), 10.1112/jlms.12375)

The classification of [3, Theorem 1.6] is missing an extra case; we thank Peter Müller for pointing this out. The omission occurs in the proof of [3, Theorem 5.4] in case 4.2. The sentence “Then (Formula presented.), which is absurd” in the last paragraph of page 332 is a result of an arithmetic error: in the case under consideration (Formula presented.). This mistake affects only the calculation of the Galois group of the trinomial (Formula presented.) over (Formula presented.) when (Formula presented.) is an algebraically closed field of characteristic 7. The Galois group of this trinomial is (Formula presented.); this can be seen by replacing the incorrect statement “Then (Formula presented.) …” with the following paragraph: Then (Formula presented.). By Theorem 3.1, the Galois group of the trinomial (Formula presented.) when (Formula presented.) either contains the alternating group or satisfies (Formula presented.). Moreover, since in the latter case (Formula presented.) is the degree 2 Frobenius, we have that either (Formula presented.) or (Formula presented.). Consider the field (Formula presented.). Over (Formula presented.), substituting (Formula presented.) shows that the Galois group of (Formula presented.) equals to the Galois group of (Formula presented.). By [1, Section 11, Case (I.2)] the Galois group of (Formula presented.) over (Formula presented.) is (Formula presented.). So the size of (Formula presented.) is at most (Formula presented.). Therefore, in this case (Formula presented.). The correct version of Theorem 1.6 should read: (Formula presented.).