diff --git a/python/dune/perftool/loopy/temporary.py b/python/dune/perftool/loopy/temporary.py
index 4957d609dffae3af3f1de44f5b4f9314ceaf5f63..1bbd59810d594badf2a429afa033fc30d09ade63 100644
--- a/python/dune/perftool/loopy/temporary.py
+++ b/python/dune/perftool/loopy/temporary.py
@@ -42,6 +42,7 @@ def _default_value(shape_impl, shape):
 def default_declaration(name, kernel, decl_info):
     shape = kernel.temporary_variables[name].shape
     shape_impl = kernel.temporary_variables[name].shape_impl
+    managed = kernel.temporary_variables[name].managed
 
     # Determine the C++ type to use for this temporary.
     t = _temporary_type(shape_impl, shape)
@@ -51,7 +52,13 @@ def default_declaration(name, kernel, decl_info):
 
     v = _default_value(shape_impl[1:], shape[1:])
     if shape_impl[0] == 'arr':
-        return '{} {}{};'.format(t, name, ''.join('[{}]'.format(s) for s in shape))
+        if managed:
+            size = 1
+            for s in shape:
+                size *= s
+            return '{} {}[{}];'.format(t, name, size)
+        else:
+            return '{} {}{};'.format(t, name, ''.join('[{}]'.format(s) for s in shape))
     if shape_impl[0] == 'vec':
         return '{} {}({}, {});'.format(t, name, shape[0], v)
     if shape_impl[0] == 'fv':
@@ -91,6 +98,10 @@ class DuneTemporaryVariable(TemporaryVariable):
 
         self.custom_declaration = self.decl_method is not None
 
+        if self.managed and shape_impl is not None:
+            for impl in shape_impl:
+                assert impl == 'arr'
+
         TemporaryVariable.__init__(self, name,
                                    managed=self.managed,
                                    shape_impl=self.shape_impl,