diff --git a/include/cyclone/runtime.h b/include/cyclone/runtime.h
index 96b74023..3bc02de5 100644
--- a/include/cyclone/runtime.h
+++ b/include/cyclone/runtime.h
@@ -172,6 +172,7 @@ object Cyc_string2number2_(void *data, object cont, int argc, object str, ...);
 int binstr2int(const char *str);
 int octstr2int(const char *str);
 object Cyc_string_append(void *data, object cont, int argc, object str1, ...);
+object Cyc_string_append2(void *data, object cont, int argc, object str1, object str2);
 object Cyc_string_length(void *data, object str);
 object Cyc_string_byte_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 bc0ce84c..86fb5d60 100644
--- a/runtime.c
+++ b/runtime.c
@@ -2245,38 +2245,35 @@ object Cyc_string_append(void *data, object cont, int _argc, object str1, ...)
   Cyc_string_append_va_list(data, _argc);
 }
 
-// TODO:
-//object Cyc_string_append2(void *data, object cont, int _argc, object str1, object str2)
-//{
-//    int i = 0, total_cp = 0, total_len = 1;
-//    int *len = alloca(sizeof(int) * argc);
-//    char *buffer, *bufferp, **str = alloca(sizeof(char *) * argc);
-//    object tmp;
-//    if (argc > 0) {
-//      Cyc_check_str(data, str1);
-//      str[i] = ((string_type *)str1)->str;
-//      len[i] = string_len((str1));
-//      total_len += len[i];
-//      total_cp += string_num_cp((str1));
-//    }
-//    for (i = 1; i < argc; i++) {
-//TODO:      tmp = va_arg(ap, object);
-//      Cyc_check_str(data, tmp);
-//      str[i] = ((string_type *)tmp)->str;
-//      len[i] = string_len((tmp));
-//      total_len += len[i];
-//      total_cp += string_num_cp((tmp));
-//    }
-//    buffer = bufferp = alloca(sizeof(char) * total_len);
-//    for (i = 0; i < argc; i++) {
-//        memcpy(bufferp, str[i], len[i]);
-//        bufferp += len[i];
-//    }
-//    *bufferp = '\0';
-//    make_string(result, buffer);
-//    string_num_cp((&result)) = total_cp;
-//    _return_closcall1(data, cont, &result);
-//}
+object Cyc_string_append2(void *data, object cont, int _argc, object str1, object str2)
+{
+    int i = 0, total_cp = 0, total_len = 1;
+    int len[2];
+    char *buffer, *bufferp, *str[2];
+
+    Cyc_check_str(data, str1);
+    Cyc_check_str(data, str2);
+
+    str[0] = ((string_type *)str1)->str;
+    len[0] = string_len((str1));
+    total_len += len[0];
+    total_cp += string_num_cp((str1));
+
+    str[1] = ((string_type *)str2)->str;
+    len[1] = string_len((str2));
+    total_len += len[1];
+    total_cp += string_num_cp((str2));
+
+    buffer = bufferp = alloca(sizeof(char) * total_len);
+    for (i = 0; i < 2; i++) {
+        memcpy(bufferp, str[i], len[i]);
+        bufferp += len[i];
+    }
+    *bufferp = '\0';
+    make_string(result, buffer);
+    string_num_cp((&result)) = total_cp;
+    _return_closcall1(data, cont, &result);
+}
 
 object Cyc_string_length(void *data, object str)
 {