diff --git a/src/Makefile.am b/src/Makefile.am
index cdcd7df8b05884f731dbcb02c30a2b6a0a8e3141..26eb7f636912e69b369476ecb30eda565b1362b8 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -48,7 +48,7 @@ AM_SOURCES = space.c runner.c queue.c task.c cell.c engine.c \
 # Include files for distribution, not installation.
 nobase_noinst_HEADERS = approx_math.h atomic.h cycle.h error.h inline.h kernel_hydro.h kernel_gravity.h \
 		 vector.h runner_doiact.h runner_doiact_grav.h units.h intrinsics.h minmax.h kick.h \
-		 timestep.h \
+		 timestep.h drift.h \
 		 gravity.h gravity_io.h \
 		 gravity/Default/gravity.h gravity/Default/gravity_iact.h gravity/Default/gravity_io.h \
 		 gravity/Default/gravity_debug.h gravity/Default/gravity_part.h  \