diff --git a/mpi/halo3d-26/Makefile b/mpi/halo3d-26/Makefile
index 4da3198..8e52353 100644
--- a/mpi/halo3d-26/Makefile
+++ b/mpi/halo3d-26/Makefile
@@ -1,10 +1,11 @@
 
 CC=mpicc
 CFLAGS=-O3 -std=c99
+EXTRA_CFLAGS=-D_POSIX_C_SOURCE=200809L
 LIBS=
 
 halo3d-26: halo3d-26.c
-	$(CC) $(CFLAGS) -o $@ $< $(LIBS)
+	$(CC) $(CFLAGS) $(EXTRA_CFLAGS) -o $@ $< $(LIBS)
 
 clean:
 	rm halo3d-26
diff --git a/mpi/halo3d/Makefile b/mpi/halo3d/Makefile
index 87a06af..4314546 100644
--- a/mpi/halo3d/Makefile
+++ b/mpi/halo3d/Makefile
@@ -1,10 +1,11 @@
 
 CC=mpicc
 CFLAGS=-O3 -std=c99
+EXTRA_CFLAGS=-D_POSIX_C_SOURCE=200809L
 LIBS=
 
 halo3d: halo3d.c
-	$(CC) $(CFLAGS) -o $@ $< $(LIBS)
+	$(CC) $(CFLAGS) $(EXTRA_CFLAGS) -o $@ $< $(LIBS)
 
 clean:
 	rm halo3d
diff --git a/mpi/sweep3d/Makefile b/mpi/sweep3d/Makefile
index a5d3677..e39dbf7 100644
--- a/mpi/sweep3d/Makefile
+++ b/mpi/sweep3d/Makefile
@@ -1,10 +1,11 @@
 
 CC=mpicc
 CFLAGS=-O3 -std=c99
+EXTRA_CFLAGS=-D_POSIX_C_SOURCE=200809L
 LIBS=
 
 sweep3d: sweep3d.c
-	$(CC) $(CFLAGS) -o $@ $< $(LIBS)
+	$(CC) $(CFLAGS) $(EXTRA_CFLAGS) -o $@ $< $(LIBS)
 
 clean:
 	rm sweep3d