diff --git a/Makefile.am b/Makefile.am
index 0c0114661..98cf55880 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -54,16 +54,7 @@ CLEANFILES = $(GITREV)
 
 PHONY = gitrev
 gitrev:
-	$(AM_V_GEN)ZFS_GITREV=$$(cd $(top_srcdir) && \
-		git describe --always --long --dirty 2>/dev/null); \
-	ZFS_GITREV=$${ZFS_GITREV:-unknown}; \
-	printf '#define\tZFS_META_GITREV "%s"\n' \
-			"$${ZFS_GITREV}" >$(GITREV)~; \
-	if cmp -s $(GITREV) $(GITREV)~; then \
-		$(RM) $(GITREV)~; \
-	else \
-		mv -f $(GITREV)~ $(GITREV); \
-	fi
+	$(AM_V_GEN)$(top_srcdir)/scripts/make_gitrev.sh $(GITREV)
 
 all: gitrev
 
diff --git a/scripts/Makefile.am b/scripts/Makefile.am
index 2ef9071f1..20c2ee8cd 100644
--- a/scripts/Makefile.am
+++ b/scripts/Makefile.am
@@ -15,6 +15,7 @@ EXTRA_DIST = \
 	dkms.postbuild \
 	enum-extract.pl \
 	kmodtool \
+	make_gitrev.sh \
 	man-dates.sh \
 	paxcheck.sh \
 	zfs2zol-patch.sed \
diff --git a/scripts/make_gitrev.sh b/scripts/make_gitrev.sh
new file mode 100755
index 000000000..8db4de931
--- /dev/null
+++ b/scripts/make_gitrev.sh
@@ -0,0 +1,50 @@
+#!/bin/sh
+
+#
+# CDDL HEADER START
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+# CDDL HEADER END
+#
+
+# Copyright (c) 2018 by Delphix. All rights reserved.
+# Copyright (c) 2018 by Matthew Thode. All rights reserved.
+
+#
+# Generate zfs_gitrev.h.  Note that we need to do this for every
+# invocation of `make`, including for incremental builds.  Therefore we
+# can't use a zfs_gitrev.h.in file which would be processed only when
+# `configure` is run.
+#
+
+set -e -u
+
+top_srcdir="$(dirname "$0")/.."
+GITREV="${1:-include/zfs_gitrev.h}"
+
+# GITREV should be a relative path (relative to top_builddir)
+case "${GITREV}" in
+	/*) echo "Error: ${GITREV} should be a relative path" >&2
+	    exit 1;;
+esac
+
+ZFS_GITREV=$({ cd "${top_srcdir}" &&
+	git describe --always --long --dirty 2>/dev/null; } || :)
+ZFS_GITREV=${ZFS_GITREV:-unknown}
+
+GITREVTMP="${GITREV}~"
+printf '#define\tZFS_META_GITREV "%s"\n' "${ZFS_GITREV}" >"${GITREVTMP}"
+if cmp -s "${GITREV}" "${GITREVTMP}"
+then
+	rm -f "${GITREVTMP}"
+else
+	mv -f "${GITREVTMP}" "${GITREV}"
+fi