diff --git a/c/src/lib/librtems++/Makefile.in b/c/src/lib/librtems++/Makefile.in
index 1bad1b6d50..379bfff8fd 100644
--- a/c/src/lib/librtems++/Makefile.in
+++ b/c/src/lib/librtems++/Makefile.in
@@ -34,7 +34,7 @@ INSTALL_CHANGE = @INSTALL_CHANGE@
 # Add local stuff here using +=
 #
 
-DEFINES +=
+DEFINES += -DNO_IMPLICIT_EXTERN_C=1
 CPPFLAGS +=
 CFLAGS += $(LIBC_DEFINES)
 
diff --git a/c/src/librtems++/src/Makefile.in b/c/src/librtems++/src/Makefile.in
index 1bad1b6d50..379bfff8fd 100644
--- a/c/src/librtems++/src/Makefile.in
+++ b/c/src/librtems++/src/Makefile.in
@@ -34,7 +34,7 @@ INSTALL_CHANGE = @INSTALL_CHANGE@
 # Add local stuff here using +=
 #
 
-DEFINES +=
+DEFINES += -DNO_IMPLICIT_EXTERN_C=1
 CPPFLAGS +=
 CFLAGS += $(LIBC_DEFINES)