diff --git a/vm/math.cpp b/vm/math.cpp
index f6419dd025..45b5e71106 100644
--- a/vm/math.cpp
+++ b/vm/math.cpp
@@ -298,8 +298,8 @@ void factor_vm::primitive_bits_double() {
     return parent->name(tagged);                        \
   }
 
-/* Note that to_fixnum, unlike the others, is strict. */
-CELL_TO_FOO(to_fixnum, fixnum, bignum_to_fixnum_strict)
+CELL_TO_FOO(to_fixnum, fixnum, bignum_to_fixnum)
+CELL_TO_FOO(to_fixnum_strict, fixnum, bignum_to_fixnum_strict)
 CELL_TO_FOO(to_cell, cell, bignum_to_cell)
 CELL_TO_FOO(to_signed_8, int64_t, bignum_to_long_long)
 CELL_TO_FOO(to_unsigned_8, uint64_t, bignum_to_ulong_long)
diff --git a/vm/math.hpp b/vm/math.hpp
index 04daf74d90..7f5a634e13 100644
--- a/vm/math.hpp
+++ b/vm/math.hpp
@@ -51,7 +51,7 @@ inline double factor_vm::fixnum_to_float(cell tagged) {
 
 inline cell factor_vm::unbox_array_size() {
   cell obj = ctx->pop();
-  fixnum n = to_fixnum(obj);
+  fixnum n = to_fixnum_strict(obj);
   if (n >= 0 && n < (fixnum)array_size_max) {
     return n;
   }
diff --git a/vm/vm.hpp b/vm/vm.hpp
index 9281fdbb88..49499b5cbe 100644
--- a/vm/vm.hpp
+++ b/vm/vm.hpp
@@ -523,6 +523,7 @@ struct factor_vm {
   void primitive_double_bits();
   void primitive_bits_double();
   fixnum to_fixnum(cell tagged);
+  fixnum to_fixnum_strict(cell tagged);
   cell to_cell(cell tagged);
   cell from_signed_8(int64_t n);
   int64_t to_signed_8(cell obj);