diff --git a/parser.c b/parser.c
index 9d11d47..cd0f182 100644
--- a/parser.c
+++ b/parser.c
@@ -50,7 +50,7 @@ static void cleanupScratch(CleanupScratch* c) { c->scratch->len = c->old_len; }
 static AstSubRange listToSpan(
     Parser* p, const AstNodeIndex* list, uint32_t count) {
     SLICE_ENSURE_CAPACITY(AstNodeIndex, &p->extra_data, count);
-    memcpy(p->extra_data.arr, list, count * sizeof(AstNodeIndex));
+    memcpy(p->extra_data.arr + p->extra_data.len, list, count * sizeof(AstNodeIndex));
     p->extra_data.len += count;
     return (AstSubRange) {
         .start = p->extra_data.len - count,