diff --git a/include/ucore/dstr.h b/include/ucore/dstr.h
index 77e462d..a003983 100644
--- a/include/ucore/dstr.h
+++ b/include/ucore/dstr.h
@@ -45,12 +45,16 @@ void uc_dstr_destroy(struct DStr *str);
  */
 size_t uc_dstr_available(const struct DStr *str);
 
-/** Ensure the DStr is of at least 'len' bytes,
+/** Ensure the DStr have room for least 'len' bytes,
  *  allocating room if needed. 
  *
+ *  This includes the length of the existing string,
+ *  to ensure e.g an additional 10 bytes can be appended,
+ *  one would do uc_dstr_ensure(str, str->len + 10)
+ *
  *  @return 0 on success (!= 0 if an allocation fail)
  */
-int uc_dstr_ensure(struct DStr *str, size_t len);
+int uc_dstr_ensure(struct DStr *str, size_t total);
 
 /** Reset the DStr, setting its length to 0
  */
diff --git a/src/dstr.c b/src/dstr.c
index 59d4cbc..d0ea6a6 100644
--- a/src/dstr.c
+++ b/src/dstr.c
@@ -22,13 +22,13 @@ size_t uc_dstr_available(const struct DStr *str)
     return str->allocated - str->len;
 }
 
-int uc_dstr_ensure(struct DStr *str, size_t len)
+int uc_dstr_ensure(struct DStr *str, size_t total)
 {
-    if (str->allocated < len) {
+    if (str->allocated < total) {
         //allocate a minimum no. of bytes, and one
         //additional for the common case of nul terminating
         //the string
-        size_t new_len = UC_MAX(7U, len) + 1;
+        size_t new_len = UC_MAX(7U, total) + 1;
         char *new_str = realloc(str->str, new_len);
 
         if (new_str == NULL) {