diff --git a/libcxx/include/string b/libcxx/include/string
--- a/libcxx/include/string
+++ b/libcxx/include/string
@@ -1535,13 +1535,14 @@
     enum {__alignment = 16};
     static _LIBCPP_INLINE_VISIBILITY
     size_type __recommend(size_type __s) _NOEXCEPT
-        {
-        if (__s < __min_cap) return static_cast<size_type>(__min_cap) - 1;
-        size_type __guess = __align_it<sizeof(value_type) < __alignment ?
-                     __alignment/sizeof(value_type) : 1 > (__s+1) - 1;
-        if (__guess == __min_cap) ++__guess;
+    {
+        if (__s < __min_cap)
+            return static_cast<size_type>(__min_cap);
+        size_type __guess = __align_it<sizeof(value_type) < __alignment ? __alignment / sizeof(value_type) : 1>(__s + 1);
+        if (__guess == __min_cap + 1)
+            ++__guess;
         return __guess;
-        }
+    }
 
     inline
     void __init(const value_type* __s, size_type __sz, size_type __reserve);
@@ -1834,9 +1835,9 @@
     else
     {
         size_type __cap = __recommend(__reserve);
-        __p = __alloc_traits::allocate(__alloc(), __cap+1);
+        __p = __alloc_traits::allocate(__alloc(), __cap);
         __set_long_pointer(__p);
-        __set_long_cap(__cap+1);
+        __set_long_cap(__cap);
         __set_long_size(__sz);
     }
     traits_type::copy(_VSTD::__to_address(__p), __s, __sz);
@@ -1858,9 +1859,9 @@
     else
     {
         size_type __cap = __recommend(__sz);
-        __p = __alloc_traits::allocate(__alloc(), __cap+1);
+        __p = __alloc_traits::allocate(__alloc(), __cap);
         __set_long_pointer(__p);
-        __set_long_cap(__cap+1);
+        __set_long_cap(__cap);
         __set_long_size(__sz);
     }
     traits_type::copy(_VSTD::__to_address(__p), __s, __sz);
@@ -1933,9 +1934,9 @@
     if (__sz > max_size())
       __throw_length_error();
     size_t __cap = __recommend(__sz);
-    __p = __alloc_traits::allocate(__alloc(), __cap + 1);
+    __p = __alloc_traits::allocate(__alloc(), __cap);
     __set_long_pointer(__p);
-    __set_long_cap(__cap + 1);
+    __set_long_cap(__cap);
     __set_long_size(__sz);
   }
   traits_type::copy(_VSTD::__to_address(__p), __s, __sz + 1);
@@ -1997,9 +1998,9 @@
     else
     {
         size_type __cap = __recommend(__n);
-        __p = __alloc_traits::allocate(__alloc(), __cap+1);
+        __p = __alloc_traits::allocate(__alloc(), __cap);
         __set_long_pointer(__p);
-        __set_long_cap(__cap+1);
+        __set_long_cap(__cap);
         __set_long_size(__n);
     }
     traits_type::assign(_VSTD::__to_address(__p), __n, __c);
@@ -2128,9 +2129,9 @@
     else
     {
         size_type __cap = __recommend(__sz);
-        __p = __alloc_traits::allocate(__alloc(), __cap+1);
+        __p = __alloc_traits::allocate(__alloc(), __cap);
         __set_long_pointer(__p);
-        __set_long_cap(__cap+1);
+        __set_long_cap(__cap);
         __set_long_size(__sz);
     }
 
@@ -2222,7 +2223,7 @@
     size_type __cap = __old_cap < __ms / 2 - __alignment ?
                           __recommend(_VSTD::max(__old_cap + __delta_cap, 2 * __old_cap)) :
                           __ms - 1;
-    pointer __p = __alloc_traits::allocate(__alloc(), __cap+1);
+    pointer __p = __alloc_traits::allocate(__alloc(), __cap);
     __invalidate_all_iterators();
     if (__n_copy != 0)
         traits_type::copy(_VSTD::__to_address(__p),
@@ -2236,7 +2237,7 @@
     if (__old_cap+1 != __min_cap)
         __alloc_traits::deallocate(__alloc(), __old_p, __old_cap+1);
     __set_long_pointer(__p);
-    __set_long_cap(__cap+1);
+    __set_long_cap(__cap);
     __old_sz = __n_copy + __n_add + __sec_cp_sz;
     __set_long_size(__old_sz);
     traits_type::assign(__p[__old_sz], value_type());
@@ -2254,7 +2255,7 @@
     size_type __cap = __old_cap < __ms / 2 - __alignment ?
                           __recommend(_VSTD::max(__old_cap + __delta_cap, 2 * __old_cap)) :
                           __ms - 1;
-    pointer __p = __alloc_traits::allocate(__alloc(), __cap+1);
+    pointer __p = __alloc_traits::allocate(__alloc(), __cap);
     __invalidate_all_iterators();
     if (__n_copy != 0)
         traits_type::copy(_VSTD::__to_address(__p),
@@ -2267,7 +2268,7 @@
     if (__old_cap+1 != __min_cap)
         __alloc_traits::deallocate(__alloc(), __old_p, __old_cap+1);
     __set_long_pointer(__p);
-    __set_long_cap(__cap+1);
+    __set_long_cap(__cap);
 }
 
 // assign
@@ -3236,7 +3237,7 @@
 
     size_type __target_capacity = _VSTD::max(__requested_capacity, size());
     __target_capacity = __recommend(__target_capacity);
-    if (__target_capacity == capacity()) return;
+    if (__target_capacity == capacity() + 1) return;
 
     __shrink_or_extend(__target_capacity);
 }
@@ -3247,7 +3248,7 @@
 basic_string<_CharT, _Traits, _Allocator>::shrink_to_fit() _NOEXCEPT
 {
     size_type __target_capacity = __recommend(size());
-    if (__target_capacity == capacity()) return;
+    if (__target_capacity == capacity() + 1) return;
 
     __shrink_or_extend(__target_capacity);
 }
@@ -3262,7 +3263,7 @@
 
     pointer __new_data, __p;
     bool __was_long, __now_long;
-    if (__target_capacity == __min_cap - 1)
+    if (__target_capacity == __min_cap)
     {
         __was_long = true;
         __now_long = false;
@@ -3272,14 +3273,14 @@
     else
     {
         if (__target_capacity > __cap)
-            __new_data = __alloc_traits::allocate(__alloc(), __target_capacity+1);
+            __new_data = __alloc_traits::allocate(__alloc(), __target_capacity);
         else
         {
         #ifndef _LIBCPP_NO_EXCEPTIONS
             try
             {
         #endif // _LIBCPP_NO_EXCEPTIONS
-                __new_data = __alloc_traits::allocate(__alloc(), __target_capacity+1);
+                __new_data = __alloc_traits::allocate(__alloc(), __target_capacity);
         #ifndef _LIBCPP_NO_EXCEPTIONS
             }
             catch (...)
@@ -3301,7 +3302,7 @@
         __alloc_traits::deallocate(__alloc(), __p, __cap+1);
     if (__now_long)
     {
-        __set_long_cap(__target_capacity+1);
+        __set_long_cap(__target_capacity);
         __set_long_size(__sz);
         __set_long_pointer(__new_data);
     }