diff --git a/grudge/models/wave.py b/grudge/models/wave.py
index a8b5470070c528fe681bd13702390f1ab58fa498..36a90424a667524ed374febc56eceaa0ad42d66e 100644
--- a/grudge/models/wave.py
+++ b/grudge/models/wave.py
@@ -220,7 +220,7 @@ class VariableCoefficientWeakWaveOperator(HyperbolicOperator):
         self.source_f = source_f
 
         ones = dcoll.zeros(actx) + 1
-        self.sign = freeze(actx.np.where(c > 0, ones, -ones))
+        self.sign = freeze(actx.np.where(actx.np.greater(c, 0), ones, -ones))
 
         self.dirichlet_tag = dirichlet_tag
         self.neumann_tag = neumann_tag
@@ -338,7 +338,7 @@ class VariableCoefficientWeakWaveOperator(HyperbolicOperator):
             self.radiation_tag])
 
     def max_characteristic_velocity(self, actx, **kwargs):
-        return actx.np.fabs(thaw(self.c, actx))
+        return actx.np.abs(thaw(self.c, actx))
 
 # }}}
 
diff --git a/grudge/shortcuts.py b/grudge/shortcuts.py
index a3561bcbeedaaaafe56e5979a5eb5c9c004e4f54..d9e5fe1faf26e245e2b4a74b3f68293be51e2293 100644
--- a/grudge/shortcuts.py
+++ b/grudge/shortcuts.py
@@ -23,7 +23,7 @@ THE SOFTWARE.
 """
 
 
-def set_up_rk4(field_var_name, dt, fields, rhs, t_start=0):
+def set_up_rk4(field_var_name, dt, fields, rhs, t_start=0.0):
     from leap.rk import LSRK4MethodBuilder
     from dagrt.codegen import PythonCodeGenerator