diff --git a/src/align.c b/src/align.c
index 5fe73ff..4724f62 100644
--- a/src/align.c
+++ b/src/align.c
@@ -739,6 +739,13 @@ static void mm_align1(void *km, const mm_mapopt_t *opt, const mm_idx_t *mi, int
 			if (ez->n_cigar > 0)
 				mm_append_cigar(r, ez->n_cigar, ez->cigar);
 			if (ez->zdropped) { // truncated by Z-drop; TODO: sometimes Z-drop kicks in because the next seed placement is wrong. This can be fixed in principle.
+				if (!r->p) {
+					assert(ez->n_cigar == 0);
+					uint32_t capacity = sizeof(mm_extra_t)/4;
+					kroundup32(capacity);
+					r->p = (mm_extra_t*)calloc(capacity, 4);
+					r->p->capacity = capacity;
+				}
 				for (j = i - 1; j >= 0; --j)
 					if ((int32_t)a[as1 + j].x <= rs + ez->max_t)
 						break;