--- a/incdefs.sh
+++ b/incdefs.sh
@@ -27,7 +27,7 @@
 	printf " -D_GNU_SOURCE"
 
 	# Get list of directories searched for header files.
-	dirs=$(${CC} -E -Wp,-v -xc /dev/null 2>&1 >/dev/null | grep ^" /")
+	dirs=$(echo "" | ${CPP} -Wp,-v - 2>&1 >/dev/null | grep ^" /")
 
 	# Look for clock_adjtime().
 	for d in $dirs; do
diff --git a/makefile b/makefile
index 3c2406b..c2fadb1 100644
--- a/makefile
+++ b/makefile
@@ -40,7 +40,7 @@ OBJECTS	= $(OBJ) hwstamp_ctl.o nsm.o phc2sys.o phc_ctl.o pmc.o pmc_agent.o \
 SRC	= $(OBJECTS:.o=.c)
 DEPEND	= $(OBJECTS:.o=.d)
 srcdir	:= $(dir $(lastword $(MAKEFILE_LIST)))
-incdefs := $(shell CC="$(CC)" $(srcdir)/incdefs.sh)
+incdefs := $(shell CPP="$(CPP)" $(srcdir)/incdefs.sh)
 version := $(shell $(srcdir)/version.sh $(srcdir))
 VPATH	= $(srcdir)