diff --git a/include/cyclone/runtime.h b/include/cyclone/runtime.h
index acc1492f..b2e52ec9 100644
--- a/include/cyclone/runtime.h
+++ b/include/cyclone/runtime.h
@@ -131,7 +131,7 @@ void dispatch_string_91append(int argc, object clo, object cont, object str1, ..
 string_type Cyc_string_append(int argc, object str1, ...);
 string_type Cyc_string_append_va_list(int argc, object str1, va_list ap);
 integer_type Cyc_string_length(object str);
-string_type Cyc_substring(object str, object start, object end);
+object Cyc_substring(object cont, object str, object start, object end);
 object Cyc_string_ref(object str, object k);
 object Cyc_string_set(object str, object k, object chr);
 string_type Cyc_installation_dir();
diff --git a/include/cyclone/types.h b/include/cyclone/types.h
index 660ab958..6ceb3c33 100644
--- a/include/cyclone/types.h
+++ b/include/cyclone/types.h
@@ -193,11 +193,11 @@ typedef struct {gc_header_type hdr; tag_type tag; int len; char *str;} string_ty
 { int len = strlen(s); cs.tag = string_tag; cs.len = len; \
   cs.str = alloca(sizeof(char) * (len + 1)); \
   strcpy(cs.str, s);}
-#define make_string_with_len(cs, length, s) string_type cs; \
+#define make_string_with_len(cs, s, length) string_type cs; \
 { cs.tag = string_tag; cs.len = length; \
   cs.str = alloca(sizeof(char) * (len + 1)); \
   strcpy(cs.str, s);}
-#define make_string_noalloc(cs, length, s) string_type cs; \
+#define make_string_noalloc(cs, s, length) string_type cs; \
 { cs.tag = string_tag; cs.len = length; \
   cs.str = s; }
 // TODO: all of the dhalloc below needs to go away...
diff --git a/runtime.c b/runtime.c
index cd4de26f..5b5ddb0d 100644
--- a/runtime.c
+++ b/runtime.c
@@ -856,7 +856,7 @@ object Cyc_number2string(object cont, object n) {
     } else {
         Cyc_rt_raise2("number->string - Unexpected object", n);
     }
-    make_string_noalloc(str, strlen(buffer), buffer);
+    make_string_noalloc(str, buffer, strlen(buffer));
     return_closcall1(cont, &str);
 }
 
@@ -891,7 +891,7 @@ object Cyc_list2string(object cont, object lst){
     }
     buf[i] = '\0';
 
-    { make_string_noalloc(str, i - 1, buf);
+    { make_string_noalloc(str, buf, i - 1);
       return_closcall1(cont, &str);}
 }
 
@@ -1029,7 +1029,7 @@ object Cyc_string_ref(object str, object k) {
   return obj_char2obj(raw[idx]);
 }
 
-string_type Cyc_substring(object str, object start, object end) {
+object Cyc_substring(object cont, object str, object start, object end) {
   const char *raw;
   int s, e, len;
 
@@ -1053,8 +1053,8 @@ string_type Cyc_substring(object str, object start, object end) {
   }
 
   {
-    make_stringn(sub, raw + s, e - s);
-    return sub;
+    make_string_with_len(sub, raw + s, e - s);
+    return_closcall1(cont, sub);
   }
 }
 
@@ -1716,8 +1716,7 @@ void _string_91length(object cont, object args) {
       return_closcall1(cont, &i);}}
 void _cyc_substring(object cont, object args) {
     Cyc_check_num_args("substring", 3, args);
-    { string_type s = Cyc_substring(car(args), cadr(args), caddr(args));
-      return_closcall1(cont, &s);}}
+    Cyc_substring(cont, car(args), cadr(args), caddr(args));}
 void _cyc_string_91set_67(object cont, object args) {
     Cyc_check_num_args("string-set!", 3, args);
     { object s = Cyc_string_set(car(args), cadr(args), caddr(args));
diff --git a/scheme/cyclone/cgen.sld b/scheme/cyclone/cgen.sld
index cfb52b7d..f0f1d899 100644
--- a/scheme/cyclone/cgen.sld
+++ b/scheme/cyclone/cgen.sld
@@ -586,6 +586,7 @@
     ((eq? p 'command-line-arguments) "object")
     ((eq? p 'number->string) "object")
     ((eq? p 'symbol->string) "object")
+    ((eq? p 'substring) "object")
     ((eq? p 'make-vector) "object")
     ((eq? p 'list->string) "object")
     ((eq? p 'list->vector) "object")
@@ -617,13 +618,15 @@
 (define (prim:cont? exp)
   (and (prim? exp)
        (member exp '(Cyc-read-line apply command-line-arguments number->string 
-                     symbol->string list->string make-vector list->vector))))
+                     symbol->string list->string substring
+                     make-vector list->vector))))
 ;; TODO: this is a hack, right answer is to include information about
 ;;  how many args each primitive is supposed to take
 (define (prim:cont-has-args? exp)
   (and (prim? exp)
        (member exp '(Cyc-read-line apply number->string symbol->string 
-                     list->string make-vector list->vector))))
+                     list->string substring
+                     make-vector list->vector))))
 
 ;; Pass an integer arg count as the function's first parameter?
 (define (prim:arg-count? exp)