diff --git a/debian/rules b/debian/rules
index 59bf24b..273b989 100755
--- a/debian/rules
+++ b/debian/rules
@@ -13,6 +13,10 @@ endif
 
 LDFLAGS += -L/usr/lib/$(DEB_HOST_MULTIARCH)/nss
 
+# Deterministic "build number". Format is defined in ./buildnum.pl
+BUILD_DATE := $(shell dpkg-parsechangelog --show-field Date)
+BUILDNUM := $(shell date --date="$(BUILD_DATE)" +%Y.%j.%H%M)
+
 override_dh_auto_configure:
 	dh_auto_configure -- \
 		--disable-rpath \
@@ -21,6 +25,9 @@ override_dh_auto_configure:
 		--with-initddir=/etc/init.d \
 		--with-apxs=/usr/bin/apxs2
 
+override_dh_auto_build:
+	dh_auto_build -- BUILDNUM=$(BUILDNUM)
+
 override_dh_auto_install:
 	dh_auto_install --destdir=$(CURDIR)/debian/tmp