Index: src/Makefile.am
===================================================================
--- src/Makefile.am.orig	2014-10-25 14:42:43.000000000 +0200
+++ src/Makefile.am	2015-02-19 10:22:03.273114977 +0100
@@ -204,14 +204,14 @@ code-to-errno.h: Makefile mkerrnos.awk e
 # It is correct to use $(CPP).  We want the host's idea of the error codes.
 mkerrcodes.h: Makefile mkerrcodes.awk $(gpg_extra_headers)
 	$(AWK) -f $(srcdir)/mkerrcodes1.awk $(srcdir)/errnos.in >_$@
-	$(CPP) $(CPPFLAGS) $(extra_cppflags) _$@ | grep GPG_ERR_ | \
+	$(CPP) -P $(CPPFLAGS) $(extra_cppflags) _$@ | grep GPG_ERR_ | \
                $(AWK) -f $(srcdir)/mkerrcodes.awk >$@
 	-rm _$@
 
 if HAVE_W32CE_SYSTEM
 # It is correct to use $(CPP).  We want the host's idea of the error codes.
 mkw32errmap.tab.h: Makefile mkw32errmap.c
-	$(CPP) -DRESOLVE_MACROS $(srcdir)/mkw32errmap.c | \
+	$(CPP) -P -DRESOLVE_MACROS $(srcdir)/mkw32errmap.c | \
 	      grep '{&mkw32errmap_marker' >$@
 mkw32errmap.map.c: mkw32errmap
 	./mkw32errmap --map > $@
@@ -227,7 +227,7 @@ endif
 # the data is really to be preprocessed.
 gpg-error.def: Makefile gpg-error.def.in
 	cat $(srcdir)/gpg-error.def.in >_$@.h
-	$(CPP) $(DEFAULT_INCLUDES) $(INCLUDES) $(extra_cppflags) _$@.h | \
+	$(CPP) -P $(DEFAULT_INCLUDES) $(INCLUDES) $(extra_cppflags) _$@.h | \
 	  grep -v '^#' >$@
 	-rm _$@.h
 
Index: src/Makefile.in
===================================================================
--- src/Makefile.in.orig	2015-01-26 10:34:10.000000000 +0100
+++ src/Makefile.in	2015-02-19 10:22:42.318558424 +0100
@@ -1227,13 +1227,13 @@ code-to-errno.h: Makefile mkerrnos.awk e
 # It is correct to use $(CPP).  We want the host's idea of the error codes.
 mkerrcodes.h: Makefile mkerrcodes.awk $(gpg_extra_headers)
 	$(AWK) -f $(srcdir)/mkerrcodes1.awk $(srcdir)/errnos.in >_$@
-	$(CPP) $(CPPFLAGS) $(extra_cppflags) _$@ | grep GPG_ERR_ | \
+	$(CPP) -P $(CPPFLAGS) $(extra_cppflags) _$@ | grep GPG_ERR_ | \
                $(AWK) -f $(srcdir)/mkerrcodes.awk >$@
 	-rm _$@
 
 # It is correct to use $(CPP).  We want the host's idea of the error codes.
 @HAVE_W32CE_SYSTEM_TRUE@mkw32errmap.tab.h: Makefile mkw32errmap.c
-@HAVE_W32CE_SYSTEM_TRUE@	$(CPP) -DRESOLVE_MACROS $(srcdir)/mkw32errmap.c | \
+@HAVE_W32CE_SYSTEM_TRUE@	$(CPP) -P -DRESOLVE_MACROS $(srcdir)/mkw32errmap.c | \
 @HAVE_W32CE_SYSTEM_TRUE@	      grep '{&mkw32errmap_marker' >$@
 @HAVE_W32CE_SYSTEM_TRUE@mkw32errmap.map.c: mkw32errmap
 @HAVE_W32CE_SYSTEM_TRUE@	./mkw32errmap --map > $@
@@ -1247,7 +1247,7 @@ mkerrcodes.h: Makefile mkerrcodes.awk $(
 # the data is really to be preprocessed.
 gpg-error.def: Makefile gpg-error.def.in
 	cat $(srcdir)/gpg-error.def.in >_$@.h
-	$(CPP) $(DEFAULT_INCLUDES) $(INCLUDES) $(extra_cppflags) _$@.h | \
+	$(CPP) -P $(DEFAULT_INCLUDES) $(INCLUDES) $(extra_cppflags) _$@.h | \
 	  grep -v '^#' >$@
 	-rm _$@.h