diff --git a/src/vm/vector_functions.cpp b/src/vm/vector_functions.cpp
index 1a1ca01..dbf2436 100644
--- a/src/vm/vector_functions.cpp
+++ b/src/vm/vector_functions.cpp
@@ -74,7 +74,7 @@ double vtype_t::lmul() {
     int8_t signed_vlmul = (vlmul >> 2) ? 0b11111000 | vlmul : vlmul;
     return pow(2, signed_vlmul);
 }
-bool vmask_view::operator[](size_t idx) {
+bool vmask_view::operator[](size_t idx) const {
     assert(idx < elem_count);
     return *(start + idx / 8) & (1U << (idx % 8));
 }