diff --git a/repos/libports/include/stdcxx/bits/c++config.h b/repos/libports/include/stdcxx/bits/c++config.h
index 6af028a60..3040d3056 100644
--- a/repos/libports/include/stdcxx/bits/c++config.h
+++ b/repos/libports/include/stdcxx/bits/c++config.h
@@ -1210,12 +1210,12 @@ namespace std
 
 /* Define if C99 functions or macros from <wchar.h>, <math.h>, <complex.h>,
    <stdio.h>, and <stdlib.h> can be used or exposed. */
-/* #undef _GLIBCXX_USE_C99 */
+#define _GLIBCXX_USE_C99 1
 
 /* Define if C99 functions in <complex.h> should be used in <complex>. Using
    compiler builtins for these functions requires corresponding C99 library
    functions to be present. */
-/* #undef _GLIBCXX_USE_C99_COMPLEX */
+#define _GLIBCXX_USE_C99_COMPLEX 1
 
 /* Define if C99 functions in <complex.h> should be used in <tr1/complex>.
    Using compiler builtins for these functions requires corresponding C99
diff --git a/repos/libports/lib/import/import-libc.mk b/repos/libports/lib/import/import-libc.mk
index eac3c43a1..0af5f8778 100644
--- a/repos/libports/lib/import/import-libc.mk
+++ b/repos/libports/lib/import/import-libc.mk
@@ -44,6 +44,11 @@ INC_DIR += $(LIBC_ARCH_INC_DIR)
 #
 CC_OPT += -D__FreeBSD__=8
 
+#
+# Provide C99 API functions (needed for C++11 in stdcxx at least)
+#
+CC_OPT += -D__ISO_C_VISIBLE=1999
+
 #
 # Prevent gcc-4.4.5 from generating code for the family of 'sin' and 'cos'
 # functions because the gcc-generated code would actually call 'sincos'