diff --git a/src/backend_x64/reg_alloc.cpp b/src/backend_x64/reg_alloc.cpp
index 765db4dd..9ffbe8b6 100644
--- a/src/backend_x64/reg_alloc.cpp
+++ b/src/backend_x64/reg_alloc.cpp
@@ -341,9 +341,9 @@ HostLoc RegAlloc::SelectARegister(HostLocList desired_locations) const {
     return candidates.front();
 }
 
-boost::optional<HostLoc> RegAlloc::ValueLocation(IR::Inst* value) const {
+boost::optional<HostLoc> RegAlloc::ValueLocation(const IR::Inst* value) const {
     for (size_t i = 0; i < HostLocCount; i++)
-        for (IR::Inst* v : hostloc_info[i].values)
+        for (const IR::Inst* v : hostloc_info[i].values)
             if (v == value)
                 return boost::make_optional<HostLoc>(static_cast<HostLoc>(i));
 
diff --git a/src/backend_x64/reg_alloc.h b/src/backend_x64/reg_alloc.h
index cfd829a1..a48e71af 100644
--- a/src/backend_x64/reg_alloc.h
+++ b/src/backend_x64/reg_alloc.h
@@ -136,7 +136,7 @@ public:
 
 private:
     HostLoc SelectARegister(HostLocList desired_locations) const;
-    boost::optional<HostLoc> ValueLocation(IR::Inst* value) const;
+    boost::optional<HostLoc> ValueLocation(const IR::Inst* value) const;
     bool IsRegisterOccupied(HostLoc loc) const;
     bool IsRegisterAllocated(HostLoc loc) const;
     bool IsLastUse(IR::Inst* inst) const;