diff --git a/Makefile.in b/Makefile.in
index 9a54a94..0605acc 100644
--- a/Makefile.in
+++ b/Makefile.in
@@ -31,7 +31,8 @@ INFODIR=@INFODIR@
 
 CC = @CC@
 CCWARNFLAGS = @CCWARNFLAGS@
-OPTFLAGS = @CFLAGS@ @EXTRA_DEFS@
+OPTFLAGS = @CFLAGS@
+CPPFLAGS = @CPPFLAGS@ @SYSDEFS@ @EXTRA_DEFS@
 
 DESTDIR=
 
@@ -54,13 +55,12 @@ EXTRA_SRCS = $(patsubst %.o,%.c,$(EXTRA_OBJS))
 
 CLI_SRCS = $(patsubst %.o,%.c,$(CLI_OBJS))
 
+LDFLAGS = @LDFLAGS@
 LIBS = @LIBS@
 
 EXTRA_LIBS=@EXTRA_LIBS@
 EXTRA_CLI_LIBS=@EXTRA_CLI_LIBS@
 
-DEFS=@SYSDEFS@
-
 CFLAGS = $(CCWARNFLAGS) $(OPTFLAGS)
 
 # Until we have a main procedure we can link, just build object files
@@ -75,7 +75,7 @@ chronyc : $(CLI_OBJS)
 	$(CC) $(OPTFLAGS) -o chronyc $(CLI_OBJS) $(LDFLAGS) @READLINE_LINK@ $(LIBS) $(EXTRA_CLI_LIBS)
 
 client.o : client.c
-	$(CC) $(CFLAGS) $(DEFS) @READLINE_COMPILE@ -c $<
+	$(CC) $(CFLAGS) $(CPPFLAGS) @READLINE_COMPILE@ -c $<
 
 .depend : 
 	gcc -MM $(SRCS) $(EXTRA_SRCS) > .depend
@@ -124,10 +124,10 @@ install: chronyd chronyc
 	chmod 444 $(DESTDIR)$(MANDIR)/man5/chrony.conf.5
 
 %.o : %.c
-	$(CC) $(CFLAGS) $(DEFS) -c $<
+	$(CC) $(CFLAGS) $(CPPFLAGS) -c $<
 
 %.s : %.c
-	$(CC) $(CFLAGS) $(DEFS) -S $<
+	$(CC) $(CFLAGS) $(CPPFLAGS) -S $<
 
 main.o logging.o client.o : version.h
 
diff --git a/configure b/configure
index d9f9f8a..a8dd51a 100755
--- a/configure
+++ b/configure
@@ -24,6 +24,8 @@ else
   MYCFLAGS="${CFLAGS}"
 fi
 
+MYCPPFLAGS="${CPPFLAGS}"
+
 # ======================================================================
 # FUNCTIONS
 
@@ -40,15 +42,15 @@ int main(int argc, char **argv) {
 }
 EOF
 
-  ${MYCC} ${MYCFLAGS} -c -o docheck.o docheck.c >/dev/null 2>&1
+  ${MYCC} ${MYCFLAGS} ${MYCPPFLAGS} -c -o docheck.o docheck.c >/dev/null 2>&1
   if [ $? -eq 0 ]
   then
-    ${MYCC} ${MYCFLAGS} -o docheck docheck.o >/dev/null 2>&1
+    ${MYCC} ${MYCFLAGS} ${MYCPPFLAGS} -o docheck docheck.o >/dev/null 2>&1
     if [ $? -eq 0 ]
     then
       result=0
     else
-      ${MYCC} ${MYCFLAGS} -o docheck docheck.o -lm >/dev/null 2>&1
+      ${MYCC} ${MYCFLAGS} ${MYCPPFLAGS} -o docheck docheck.o -lm >/dev/null 2>&1
       if [ $? -eq 0 ]
       then
         result=1
@@ -73,7 +75,7 @@ int main(int argc, char **argv) {
 }
 EOF
 
-  ${MYCC} ${MYCFLAGS} -c -o docheck.o docheck.c >/dev/null 2>&1
+  ${MYCC} ${MYCFLAGS} ${MYCPPFLAGS} -c -o docheck.o docheck.c >/dev/null 2>&1
   if [ $? -eq 0 ]
   then
     result=0
@@ -94,7 +96,7 @@ int main(int argc, char **argv) {
 }
 EOF
 
-  ${MYCC} ${MYCFLAGS} -c -o docheck.o docheck.c >/dev/null 2>&1
+  ${MYCC} ${MYCFLAGS} ${MYCPPFLAGS} -c -o docheck.o docheck.c >/dev/null 2>&1
   if [ $? -eq 0 ]
   then
     result=0
@@ -120,7 +122,7 @@ int main(int argc, char **argv) {
 }
 EOF
 
-  ${MYCC} ${MYCFLAGS} -c -o docheck.o docheck.c >/dev/null 2>&1
+  ${MYCC} ${MYCFLAGS} ${MYCPPFLAGS} -c -o docheck.o docheck.c >/dev/null 2>&1
   if [ $? -eq 0 ]
   then
     result=0
@@ -144,7 +146,7 @@ int main(int argc, char **argv) {
 }
 EOF
 
-  ${MYCC} ${MYCFLAGS} -c -o docheck.o docheck.c >/dev/null 2>&1
+  ${MYCC} ${MYCFLAGS} ${MYCPPFLAGS} -c -o docheck.o docheck.c >/dev/null 2>&1
   if [ $? -eq 0 ]
   then
     result=0
@@ -195,6 +197,8 @@ Fine tuning of the installation directories:
 Some influential environment variables:
   CC          C compiler command
   CFLAGS      C compiler flags
+  CPPFLAGS    C preprocessor flags, e.g. -I<include dir> if you have
+              headers in a nonstandard directory <include dir>
   LDFLAGS     linker flags, e.g. -L<lib dir> if you have libraries in a
               nonstandard directory <lib dir>
 
@@ -442,7 +446,9 @@ sed -e "s%@EXTRA_OBJECTS@%${EXTRA_OBJECTS}%;\
 	s%@CC@%${MYCC}%;\
 	s%@CFLAGS@%${MYCFLAGS}%;\
 	s%@CCWARNFLAGS@%${CCWARNFLAGS}%;\
+	s%@CPPFLAGS@%${CPPFLAGS}%;\
 	s%@LIBS@%${LIBS}%;\
+	s%@LDFLAGS@%${LDFLAGS}%;\
 	s%@EXTRA_LIBS@%${EXTRA_LIBS}%;\
 	s%@SYSDEFS@%${SYSDEFS}%;\
 	s%@EXTRA_DEFS@%${EXTRA_DEFS}%;\