diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000000..5338a222d0
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,3 @@
+[submodule "RecogExtSquareGreenhill"]
+	path = RecogExtSquareGreenhill
+	url = https://github.com/wucas/RecogExtSquareGreenhill.git
diff --git a/RecogExtSquareGreenhill b/RecogExtSquareGreenhill
new file mode 160000
index 0000000000..c59d384762
--- /dev/null
+++ b/RecogExtSquareGreenhill
@@ -0,0 +1 @@
+Subproject commit c59d384762012520bc39884fca5f6c2dd0875ebd
diff --git a/tst/testinstall/recogextsq.tst b/tst/testinstall/recogextsq.tst
new file mode 100644
index 0000000000..239a795ebe
--- /dev/null
+++ b/tst/testinstall/recogextsq.tst
@@ -0,0 +1,5 @@
+gap> START_TEST("recogextsq.tst");
+gap> ReadGapRoot("RecogExtSquareGreenhill/TestRecogExtSquareOfMatrix.g");
+gap> testExtSquareMat();
+true
+gap> STOP_TEST("recogextsq.tst");
\ No newline at end of file