diff --git a/src/mathed/MathMacro.cpp b/src/mathed/MathMacro.cpp
index a2dc9cea2d..e40b958c45 100644
--- a/src/mathed/MathMacro.cpp
+++ b/src/mathed/MathMacro.cpp
@@ -254,6 +254,22 @@ bool MathMacro::idxLast(Cursor & cur) const
 }
 
 
+bool MathMacro::idxUpDown(Cursor & cur, bool up) const
+{
+	if (up) {
+		if (cur.idx() == 0)
+			return false;
+		--cur.idx();
+	} else {
+		if (cur.idx() + 1 >= nargs())
+			return false;
+		++cur.idx();
+	}
+	cur.pos() = cell(cur.idx()).x2pos(cur.x_target());
+	return true;
+}
+
+
 bool MathMacro::notifyCursorLeaves(Cursor & cur)
 {
 	cur.updateFlags(Update::Force);
diff --git a/src/mathed/MathMacro.h b/src/mathed/MathMacro.h
index 6193ec62fe..8e9f1b23d0 100644
--- a/src/mathed/MathMacro.h
+++ b/src/mathed/MathMacro.h
@@ -48,6 +48,8 @@ public:
 	/// target pos when we enter the inset from the right by pressing "Left"
 	bool idxLast(Cursor &) const;
 	///
+	bool idxUpDown(Cursor & cur, bool up) const;
+	///
 	virtual bool notifyCursorLeaves(Cursor &);
 	///
 	docstring name() const;