diff --git a/include/cyclone/runtime.h b/include/cyclone/runtime.h
index 86a85507..06a4ff6a 100644
--- a/include/cyclone/runtime.h
+++ b/include/cyclone/runtime.h
@@ -191,7 +191,6 @@ object Cyc_string2number_(void *d, object cont, object str);
 object Cyc_string2number2_(void *data, object cont, int argc, object str, ...);
 int binstr2int(const char *str);
 int octstr2int(const char *str);
-int hexstr2int(const char *str);
 object Cyc_string_append(void *data, object cont, int argc, object str1, ...);
 object Cyc_string_length(void *data, object str);
 object Cyc_substring(void *data, object cont, object str, object start,
diff --git a/runtime.c b/runtime.c
index b358cb79..de207ce8 100644
--- a/runtime.c
+++ b/runtime.c
@@ -1430,13 +1430,13 @@ object Cyc_string2number2_(void *data, object cont, int argc, object str, ...)
     base_num = unbox_number(base);
     Cyc_check_str(data, str);
     if (base_num == 2) {
-      result = binstr2int(string_str(str));
+      result = (int)strtol(string_str(str), NULL, 2);
       _return_closcall1(data, cont, obj_int2obj(result));
     } else if (base_num == 8) {
-      result = octstr2int(string_str(str));
+      result = (int)strtol(string_str(str), NULL, 8);
       _return_closcall1(data, cont, obj_int2obj(result));
     } else if (base_num == 16) {
-      result = hexstr2int(string_str(str));
+      result = (int)strtol(string_str(str), NULL, 16);
       _return_closcall1(data, cont, obj_int2obj(result));
     }
   }
@@ -1546,23 +1546,6 @@ int octstr2int(const char *str)
   return num;
 }
 
-int hexstr2int(const char *str)
-{
-  int num = 0;
-  while (*str) {
-    num <<= 4;
-    if (*str >= 'A' && *str <= 'F') {
-      num += (((*str) - 'A') + 10);
-    } else if (*str >= 'a' && *str <= 'f') {
-      num += (((*str) - 'a') + 10);
-    } else {
-      num += ((*str) - '0');
-    }
-    *str++;
-  }
-  return num;
-}
-
 object Cyc_string_cmp(void *data, object str1, object str2)
 {
   Cyc_check_str(data, str1);