diff --git a/gdk/fallback-c89.c b/gdk/fallback-c89.c
index 4baf797f3c..e9adc5eba8 100644
--- a/gdk/fallback-c89.c
+++ b/gdk/fallback-c89.c
@@ -17,6 +17,8 @@
  * License along with this library. If not, see <http://www.gnu.org/licenses/>.
  */
 
+#include "config.h"
+
 #include <float.h>
 
 #ifndef HAVE_DECL_ISNAN
diff --git a/gtk/fallback-c89.c b/gtk/fallback-c89.c
index df28048feb..61536771ee 100644
--- a/gtk/fallback-c89.c
+++ b/gtk/fallback-c89.c
@@ -17,8 +17,10 @@
  * License along with this library. If not, see <http://www.gnu.org/licenses/>.
  */
 
+#include "config.h"
+
 #include <math.h>
- 
+
 /* Workaround for round() for non-GCC/non-C99 compilers */
 #ifndef HAVE_ROUND
 static inline double