diff --git a/config/ChangeLog b/config/ChangeLog
index 7d000625c76..f4152c4ebff 100644
--- a/config/ChangeLog
+++ b/config/ChangeLog
@@ -1,3 +1,8 @@
+2014-04-25  Marc Glisse  <marc.glisse@inria.fr>
+
+	PR target/43538
+	* mt-gnu: Don't reset CXXFLAGS_FOR_TARGET.
+
 2013-11-29  Marek Polacek  <polacek@redhat.com>
 
 	* bootstrap-ubsan.mk (POSTSTAGE1_LDFLAGS): Remove -lpthread -ldl.
diff --git a/config/mt-gnu b/config/mt-gnu
index 15bf4171603..5c696f51b0b 100644
--- a/config/mt-gnu
+++ b/config/mt-gnu
@@ -1 +1 @@
-CXXFLAGS_FOR_TARGET = $(CXXFLAGS) -D_GNU_SOURCE
+CXXFLAGS_FOR_TARGET += -D_GNU_SOURCE