diff --git a/libphobos/ChangeLog b/libphobos/ChangeLog
index 869d96ea77ddf1bff43540b71f3998c77a56deae..60d39c9bb77b8153b249b207e41e819dc392152f 100644
--- a/libphobos/ChangeLog
+++ b/libphobos/ChangeLog
@@ -1,3 +1,10 @@
+2019-04-16  Iain Buclaw  <ibuclaw@gdcproject.org>
+
+	* config.h.in: Regenerate.
+	* configure: Regenerate.
+	* m4/druntime/libraries.m4 (DRUNTIME_LIBRARIES_BACKTRACE): Set
+	CPPFLAGS correctly for backtrace support test.
+
 2019-04-14  Rainer Orth  <ro@CeBiTec.Uni-Bielefeld.DE>
 
 	* configure.tgt (LIBPHOBOS_SUPPORTED): Default to no.
diff --git a/libphobos/config.h.in b/libphobos/config.h.in
index 19266b3b5e41b6282734d91a14a107f4297731c8..0249849c890b213c8931e9493ef263a4a7c64000 100644
--- a/libphobos/config.h.in
+++ b/libphobos/config.h.in
@@ -54,3 +54,35 @@
 
 /* Define to 1 if you have the ANSI C header files. */
 #undef STDC_HEADERS
+
+/* Enable extensions on AIX 3, Interix.  */
+#ifndef _ALL_SOURCE
+# undef _ALL_SOURCE
+#endif
+/* Enable GNU extensions on systems that have them.  */
+#ifndef _GNU_SOURCE
+# undef _GNU_SOURCE
+#endif
+/* Enable threading extensions on Solaris.  */
+#ifndef _POSIX_PTHREAD_SEMANTICS
+# undef _POSIX_PTHREAD_SEMANTICS
+#endif
+/* Enable extensions on HP NonStop.  */
+#ifndef _TANDEM_SOURCE
+# undef _TANDEM_SOURCE
+#endif
+/* Enable general extensions on Solaris.  */
+#ifndef __EXTENSIONS__
+# undef __EXTENSIONS__
+#endif
+
+
+/* Define to 1 if on MINIX. */
+#undef _MINIX
+
+/* Define to 2 if the system does not provide POSIX.1 features except with
+   this defined. */
+#undef _POSIX_1_SOURCE
+
+/* Define to 1 if you need to in order for `stat' and other things to work. */
+#undef _POSIX_SOURCE
diff --git a/libphobos/configure b/libphobos/configure
index 87e4e4a7c9b19339bc0d2f30321b75508633ec36..8079a73527dfd8c6876f4f9693cec5bb89ab9855 100755
--- a/libphobos/configure
+++ b/libphobos/configure
@@ -14838,7 +14838,7 @@ fi
     LIBBACKTRACE=../../libbacktrace/libbacktrace.la
 
     gdc_save_CPPFLAGS=$CPPFLAGS
-    CPPFLAGS+=" -I../libbacktrace "
+    CPPFLAGS="$CPPFLAGS -I../libbacktrace "
 
     ac_fn_c_check_header_mongrel "$LINENO" "backtrace-supported.h" "ac_cv_header_backtrace_supported_h" "$ac_includes_default"
 if test "x$ac_cv_header_backtrace_supported_h" = xyes; then :
diff --git a/libphobos/m4/druntime/libraries.m4 b/libphobos/m4/druntime/libraries.m4
index 6e81fd99e4b0f019fb19016e47ca300f71897a03..a7aab4dd88bee35c6451a337a159c1057102f7e0 100644
--- a/libphobos/m4/druntime/libraries.m4
+++ b/libphobos/m4/druntime/libraries.m4
@@ -178,7 +178,7 @@ AC_DEFUN([DRUNTIME_LIBRARIES_BACKTRACE],
     LIBBACKTRACE=../../libbacktrace/libbacktrace.la
 
     gdc_save_CPPFLAGS=$CPPFLAGS
-    CPPFLAGS+=" -I../libbacktrace "
+    CPPFLAGS="$CPPFLAGS -I../libbacktrace "
 
     AC_CHECK_HEADER(backtrace-supported.h, have_libbacktrace_h=true,
       have_libbacktrace_h=false)