diff --git a/cgen.scm b/cgen.scm
index e85d2689..2d3ce8ff 100644
--- a/cgen.scm
+++ b/cgen.scm
@@ -400,7 +400,7 @@
      ((eq? p 'Cyc-set-cvar!)         "Cyc_set_cvar")
      ((eq? p 'Cyc-cvar?)             "Cyc_is_cvar")
      ((eq? p 'Cyc-has-cycle?)        "Cyc_has_cycle")
-     ((eq? p '+)                     "__sum")
+     ((eq? p '+)                     "Cyc_sum")
      ((eq? p '-)                     "__sub")
      ((eq? p '*)                     "__mul")
      ((eq? p '/)                     "__div")
@@ -554,6 +554,7 @@
     ((eq? p 'open-input-file) "port_type")
     ((eq? p 'length) "integer_type")
     ((eq? p 'char->integer) "integer_type")
+    ((eq? p '+) "common_type")
     ((eq? p 'string->number) "common_type")
     ((eq? p 'list->string) "string_type")
 ;    ((eq? p 'string->list) "object")
diff --git a/runtime.h b/runtime.h
index f5dbcbc4..a6d7da56 100644
--- a/runtime.h
+++ b/runtime.h
@@ -94,6 +94,7 @@ static object Cyc_is_char(object o);
 static object Cyc_is_procedure(object o);
 static object Cyc_is_eof_object(object o);
 static object Cyc_is_cvar(object o);
+static common_type Cyc_sum(object x, object y);
 static int equal(object,object);
 static list assq(object,list);
 static object get(object,object);
@@ -782,7 +783,6 @@ static object __halt(object obj) {
     return nil;
 }
 
-#define __sum(c,x,y) integer_type c; c.tag = integer_tag; c.value = (((integer_type *)(x))->value + ((integer_type *)(y))->value);
 #define __mul(c,x,y) integer_type c; c.tag = integer_tag; c.value = (((integer_type *)(x))->value * ((integer_type *)(y))->value);
 #define __sub(c,x,y) integer_type c; c.tag = integer_tag; c.value = (((integer_type *)(x))->value - ((integer_type *)(y))->value);
 #define __div(c,x,y) integer_type c; c.tag = integer_tag; c.value = (((integer_type *)(x))->value / ((integer_type *)(y))->value);
@@ -939,8 +939,8 @@ static void _set_91cdr_67(object cont, object args) {
 static void _Cyc_91has_91cycle_127(object cont, object args) { 
     return_funcall1(cont, Cyc_has_cycle(car(args))); }
 static void __87(object cont, object args) {
-    __sum(i, car(args), cadr(args));
-    return_funcall1(cont, &i); }
+    common_type n = Cyc_sum(car(args), cadr(args));
+    return_funcall1(cont, &n); }
 static void __91(object cont, object args) {
     __sub(i, car(args), cadr(args));
     return_funcall1(cont, &i); }