diff --git a/frappy/datatypes.py b/frappy/datatypes.py
index 8162edc..86cf008 100644
--- a/frappy/datatypes.py
+++ b/frappy/datatypes.py
@@ -844,9 +844,16 @@ class ArrayOf(DataType):
         return self(value)
 
     def format_value(self, value, unit=None):
+        innerunit = ''
         if unit is None:
-            unit = self.unit or self.members.unit
-        res = '[%s]' % (', '.join([self.members.format_value(elem, '') for elem in value]))
+            members = self.members
+            while isinstance(members, ArrayOf):
+                members = members.members
+            if members.unit:
+                unit = members.unit
+            else:
+                innerunit = None
+        res = '[%s]' % (', '.join([self.members.format_value(elem, innerunit) for elem in value]))
         if unit:
             return ' '.join([res, unit])
         return res
diff --git a/test/test_datatypes.py b/test/test_datatypes.py
index 17bfbf6..82cda7c 100644
--- a/test/test_datatypes.py
+++ b/test/test_datatypes.py
@@ -420,6 +420,9 @@ def test_ArrayOf():
     dt = ArrayOf(EnumType('myenum', single=0), 5)
     copytest(dt)
 
+    dt = ArrayOf(ArrayOf(FloatRange(unit='m')))
+    assert dt.format_value([[0, 1], [2, 3]]) == '[[0, 1], [2, 3]] m'
+
 
 def test_TupleOf():
     # test constructor catching illegal arguments