diff --git a/src/library/compiler/ir_interpreter.cpp b/src/library/compiler/ir_interpreter.cpp
index 2aa1accc3e..03b3c48146 100644
--- a/src/library/compiler/ir_interpreter.cpp
+++ b/src/library/compiler/ir_interpreter.cpp
@@ -172,6 +172,7 @@ option_ref<decl> find_ir_decl(environment const & env, name const & n) {
 }
 
 static string_ref * g_mangle_prefix = nullptr;
+static string_ref * g_boxed_suffix = nullptr;
 static string_ref * g_boxed_mangled_suffix = nullptr;
 
 // reuse the compiler's name mangling to compute native symbol names
@@ -826,6 +827,7 @@ public:
     }
 
     object * call_boxed(name const & fn, object ** args) {
+    /** Like `call`, but taking (owned) `object *`s instead of `arg`s. */
         symbol_cache_entry e = lookup_symbol(fn);
         unsigned n = decl_params(e.m_decl).size();
         object * r;
@@ -834,26 +836,17 @@ public:
             // directly call boxed function, nothing more to do
             r = curry(e.m_addr, n, args);
         } else {
-            // equivalent code to boxed stubs generated by the compiler: unbox args, box result, decrement borrowed args
-
-            if (decl_tag(e.m_decl) == decl_kind::Extern) {
-                throw exception(sstream() << "unexpected external declaration '" << fn << "'");
+            decl d = e.m_decl;
+            if (option_ref<decl> d_boxed = find_ir_decl(m_env, fn + *g_boxed_suffix)) {
+                d = *d_boxed.get();
             }
+            // `d` now has a boxed signature
             // evaluate args in old stack frame
             for (unsigned i = 0; i < n; i++) {
-                type t = param_type(decl_params(e.m_decl)[i]);
-                m_arg_stack.push_back(unbox_t(args[i], t));
-                if (type_is_scalar(t)) {
-                    dec(args[i]);
-                }
+                m_arg_stack.push_back(args[i]);
             }
             push_frame(e.m_decl, 0);
-            r = box_t(eval_body(decl_fun_body(e.m_decl)), decl_type(e.m_decl));
-            for (size_t i = 0; i < n; i++) {
-                if (param_borrow(decl_params(e.m_decl)[i])) {
-                    dec(args[i]);
-                }
-            }
+            r = eval_body(decl_fun_body(e.m_decl)).m_obj;
         }
         pop_frame(r, decl_type(e.m_decl));
         return r;
@@ -905,6 +898,7 @@ uint32 run_main(environment const & env, int argv, char * argc[]) {
 
 void initialize_ir_interpreter() {
     ir::g_mangle_prefix = new string_ref("l_");
+    ir::g_boxed_suffix = new string_ref("_boxed");
     ir::g_boxed_mangled_suffix = new string_ref("___boxed");
     DEBUG_CODE({
         register_trace_class({"interpreter"});
@@ -915,6 +909,7 @@ void initialize_ir_interpreter() {
 
 void finalize_ir_interpreter() {
     delete ir::g_boxed_mangled_suffix;
+    delete ir::g_boxed_suffix;
     delete ir::g_mangle_prefix;
 }
 }