diff --git a/dolo/compiler/symbolic.py b/dolo/compiler/symbolic.py
index ca758df9..d7ec8c19 100644
--- a/dolo/compiler/symbolic.py
+++ b/dolo/compiler/symbolic.py
@@ -219,6 +219,8 @@ def eval_scalar(tree):
         elif isinstance(tree, ast.UnaryOp):
             if isinstance(tree.op, ast.USub):
                 return -tree.operand.n
+            if isinstance(tree.op, ast.UAdd):
+                return tree.operand.n
         else:
             raise Exception("Don't know how to do that.")
     except:
diff --git a/dolo/tests/test_rbc.py b/dolo/tests/test_rbc.py
index b1c63463..e03f59f5 100644
--- a/dolo/tests/test_rbc.py
+++ b/dolo/tests/test_rbc.py
@@ -21,9 +21,9 @@ def test_rbc_model():
     pol = evaluate_policy(model, dr, verbose=True)
     polg = evaluate_policy(model, drg, verbose=True)
 
-    sim = simulate(model, dr, n_exp=0) # irf
-    sim = simulate(model, dr, n_exp=2) # stochastic simulations (2 draws)
-    # extract first simulation
+    sim = simulate(model, dr, n_exp=0)  # irf
+    sim = simulate(model, dr, n_exp=2)  # stochastic simulations (2 draws)
+                                        # extract first simulation
     assert(len(sim[0]['k'])==40)