diff --git a/image_analysis/scale_merge/HKLKey.cpp b/image_analysis/scale_merge/HKLKey.cpp
index 1cbb3852..76490f94 100644
--- a/image_analysis/scale_merge/HKLKey.cpp
+++ b/image_analysis/scale_merge/HKLKey.cpp
@@ -4,11 +4,12 @@
 #include <cmath>
 
 #include "HKLKey.h"
+#include "gemmi/symmetry.hpp"
 
-HKLKey CanonicalHKL(const Reflection &r, bool merge_friedel, const std::optional<gemmi::SpaceGroup> &sg) {
+HKLKey CanonicalHKL(const Reflection &r, bool merge_friedel, const std::optional<gemmi::SpaceGroup> &in_sg) {
     HKLKey key{r.h, r.k, r.l, true};
 
-    if (!sg.has_value()) {
+    if (!in_sg.has_value()) {
         if (!merge_friedel) {
             const HKLKey neg{-r.h, -r.k, -r.l, true};
             if (std::tie(key.h, key.k, key.l) < std::tie(neg.h, neg.k, neg.l)) {
@@ -19,8 +20,9 @@ HKLKey CanonicalHKL(const Reflection &r, bool merge_friedel, const std::optional
             }
         }
     } else {
-        const auto ops = sg->operations();
-        const gemmi::ReciprocalAsu asu(sg.get());
+        gemmi::SpaceGroup sg = in_sg.value();
+        const auto ops = sg.operations();
+        const gemmi::ReciprocalAsu asu(&sg);
 
         const gemmi::Op::Miller in{r.h, r.k, r.l};
         const auto [hkl, sign_plus] = asu.to_asu_sign(in, ops);