diff --git a/configure.ac b/configure.ac
index 8b9f8ee..3720042 100644
--- a/configure.ac
+++ b/configure.ac
@@ -35,6 +35,7 @@ if ! test -z "$with_fw_dir" ; then
    FW_DIR="$with_fw_dir"
    AC_SUBST(FW_DIR)
 fi
+AM_CONDITIONAL([WITH_FW_DIR], [! test -z "$with_fw_dir"])
 
 AC_ARG_WITH(fw-device-prefix,
 	[  --with-fw-device-prefix=<prefix>  Prefix of firewire device file names (default "fw").],
diff --git a/src/Makefile.am b/src/Makefile.am
index a62df10..79ee407 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -6,7 +6,11 @@ lib_LTLIBRARIES = libraw1394.la
 
 libraw1394_la_LDFLAGS = -version-info @lt_major@:@lt_revision@:@lt_age@
 
+if WITH_FW_DIR
 INCLUDES = -I$(FW_DIR)
+else
+INCLUDES =
+endif
 
 libraw1394_la_SOURCES =   \
 	main.c            \