diff --git a/Makefile.am b/Makefile.am
index e62f2678e..10a2c8ae2 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -211,6 +211,7 @@ EXTRA_DIST = \
 	autogen.sh \
 	bindtests \
 	cfg.mk \
+	check-mli.sh \
 	contrib/autobuild/autobuild.sh \
 	contrib/intro/libguestfs-intro.html \
 	contrib/intro/overview.png \
@@ -536,6 +537,10 @@ check-root: build-test-guests
 build-test-guests:
 	$(MAKE) -C test-data/phony-guests check
 
+# Some tests which run at the top level.
+
+TESTS = check-mli.sh
+
 # Print subdirs.
 #
 # If you want to selectively run tests, or if the test suite fails half
diff --git a/check-mli.sh b/check-mli.sh
new file mode 100755
index 000000000..9e9a89ff4
--- /dev/null
+++ b/check-mli.sh
@@ -0,0 +1,41 @@
+#!/bin/bash -
+# Check every .ml file has a corresponding .mli file.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+
+# OCaml itself doesn't require it, but getting Makefile dependencies
+# correct is impossible when some .ml files don't have a corresponding
+# .mli file.
+
+exitcode=0
+
+for f in $(
+    find -name '*.ml' |
+    grep -v builder/templates |
+    grep -v contrib/ |
+    grep -v ocaml/examples/ |
+    grep -v ocaml/t/ |
+    grep -v 'tests/automake2junit.ml$' |
+    grep -v 'bindtests.ml$' |
+    grep -v '_tests.ml$' |
+    sort
+); do
+    if [ ! -f "${f}i" ]; then
+        echo $f: missing ${f}i
+        exitcode=1
+    fi
+done
+
+exit $exitcode