diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 4e77d33b08dc..fd5dc86d9596 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,3 +1,17 @@
+2009-12-15  Paolo Carlini  <paolo.carlini@oracle.com>
+
+	PR libsdtc++/42381
+	* include/bits/stl_deque.h (_GLIBCXX_DEQUE_BUF_SIZE): Add.
+	(__deque_buf_size(size_t)): Use it.
+	* testsuite/23_containers/deque/requirements/dr438/
+	assign_neg.cc: Adjust dg-error line numbers.
+	* testsuite/23_containers/deque/requirements/dr438/
+	insert_neg.cc: Likewise.
+	* testsuite/23_containers/deque/requirements/dr438/
+	constructor_1_neg.cc: Likewise.
+	* testsuite/23_containers/deque/requirements/dr438/
+	constructor_2_neg.cc: Likewise.
+
 2009-12-15  Jonathan Wakely  <jwakely.gcc@gmail.com>
 
 	* include/std/future (unique_future::get, promise::set_value): Remove
diff --git a/libstdc++-v3/include/bits/stl_deque.h b/libstdc++-v3/include/bits/stl_deque.h
index 7f601cbf0fb0..d7589f71d7aa 100644
--- a/libstdc++-v3/include/bits/stl_deque.h
+++ b/libstdc++-v3/include/bits/stl_deque.h
@@ -72,11 +72,19 @@ _GLIBCXX_BEGIN_NESTED_NAMESPACE(std, _GLIBCXX_STD_D)
    *  This function started off as a compiler kludge from SGI, but seems to
    *  be a useful wrapper around a repeated constant expression.  The '512' is
    *  tunable (and no other code needs to change), but no investigation has
-   *  been done since inheriting the SGI code.
+   *  been done since inheriting the SGI code.  Touch _GLIBCXX_DEQUE_BUF_SIZE
+   *  only if you know what you are doing, however: changing it breaks the
+   *  binary compatibility!!
   */
+
+#ifndef _GLIBCXX_DEQUE_BUF_SIZE
+#define _GLIBCXX_DEQUE_BUF_SIZE 512
+#endif
+
   inline size_t
   __deque_buf_size(size_t __size)
-  { return __size < 512 ? size_t(512 / __size) : size_t(1); }
+  { return (__size < _GLIBCXX_DEQUE_BUF_SIZE
+	    ? size_t(_GLIBCXX_DEQUE_BUF_SIZE / __size) : size_t(1)); }
 
 
   /**
@@ -1798,6 +1806,8 @@ _GLIBCXX_BEGIN_NESTED_NAMESPACE(std, _GLIBCXX_STD_D)
     swap(deque<_Tp,_Alloc>& __x, deque<_Tp,_Alloc>& __y)
     { __x.swap(__y); }
 
+#undef _GLIBCXX_DEQUE_BUF_SIZE
+
 _GLIBCXX_END_NESTED_NAMESPACE
 
 #endif /* _STL_DEQUE_H */
diff --git a/libstdc++-v3/testsuite/23_containers/deque/requirements/dr438/assign_neg.cc b/libstdc++-v3/testsuite/23_containers/deque/requirements/dr438/assign_neg.cc
index f7439944837a..314a13f64e7a 100644
--- a/libstdc++-v3/testsuite/23_containers/deque/requirements/dr438/assign_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/deque/requirements/dr438/assign_neg.cc
@@ -18,7 +18,7 @@
 // <http://www.gnu.org/licenses/>.
 
 // { dg-do compile }
-// { dg-error "no matching" "" { target *-*-* } 1494 }
+// { dg-error "no matching" "" { target *-*-* } 1502 }
 // { dg-excess-errors "" }
 
 #include <deque>
diff --git a/libstdc++-v3/testsuite/23_containers/deque/requirements/dr438/constructor_1_neg.cc b/libstdc++-v3/testsuite/23_containers/deque/requirements/dr438/constructor_1_neg.cc
index b1136f59cf7b..2ae51b836d80 100644
--- a/libstdc++-v3/testsuite/23_containers/deque/requirements/dr438/constructor_1_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/deque/requirements/dr438/constructor_1_neg.cc
@@ -18,7 +18,7 @@
 // <http://www.gnu.org/licenses/>.
 
 // { dg-do compile }
-// { dg-error "no matching" "" { target *-*-* } 1433 }
+// { dg-error "no matching" "" { target *-*-* } 1441 }
 // { dg-excess-errors "" }
 
 #include <deque>
diff --git a/libstdc++-v3/testsuite/23_containers/deque/requirements/dr438/constructor_2_neg.cc b/libstdc++-v3/testsuite/23_containers/deque/requirements/dr438/constructor_2_neg.cc
index 8752a7e7b10b..22bb275068b3 100644
--- a/libstdc++-v3/testsuite/23_containers/deque/requirements/dr438/constructor_2_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/deque/requirements/dr438/constructor_2_neg.cc
@@ -18,7 +18,7 @@
 // <http://www.gnu.org/licenses/>.
 
 // { dg-do compile }
-// { dg-error "no matching" "" { target *-*-* } 1433 }
+// { dg-error "no matching" "" { target *-*-* } 1441 }
 // { dg-excess-errors "" }
 
 #include <deque>
diff --git a/libstdc++-v3/testsuite/23_containers/deque/requirements/dr438/insert_neg.cc b/libstdc++-v3/testsuite/23_containers/deque/requirements/dr438/insert_neg.cc
index 8cf322e82198..cdacae483f93 100644
--- a/libstdc++-v3/testsuite/23_containers/deque/requirements/dr438/insert_neg.cc
+++ b/libstdc++-v3/testsuite/23_containers/deque/requirements/dr438/insert_neg.cc
@@ -18,7 +18,7 @@
 // <http://www.gnu.org/licenses/>.
 
 // { dg-do compile }
-// { dg-error "no matching" "" { target *-*-* } 1578 }
+// { dg-error "no matching" "" { target *-*-* } 1586 }
 // { dg-excess-errors "" }
 
 #include <deque>