diff --git a/grudge/models/wave.py b/grudge/models/wave.py
index 4057adb98c849a7543a6fb2a862c38cac9c69868..ce98e59c061a8db62efaf051a7ae1bb7581dbe6f 100644
--- a/grudge/models/wave.py
+++ b/grudge/models/wave.py
@@ -103,7 +103,7 @@ class StrongWaveOperator(HyperbolicOperator):
                 np.dot(v.int, normal),
                 u.int * normal) - flux_weak
 
-        return -self.c*flux_strong
+        return self.c*flux_strong
 
     def sym_operator(self):
         d = self.ambient_dim
diff --git a/grudge/symbolic/mappers/__init__.py b/grudge/symbolic/mappers/__init__.py
index c36f86ab09d8879193b3fa02089e5eb9b58a1885..3b8e764d186f08a5f8bd859caca1acfe1053b4e9 100644
--- a/grudge/symbolic/mappers/__init__.py
+++ b/grudge/symbolic/mappers/__init__.py
@@ -529,7 +529,7 @@ class GlobalToReferenceMapper(CSECachingMapperMixin, IdentityMapper):
                 1/jac_in * self.rec(expr.field))
 
         elif isinstance(expr.op, op.FaceMassOperator):
-            jac_in_surf = - sym.area_element(self.ambient_dim, self.dim - 1,
+            jac_in_surf = sym.area_element(self.ambient_dim, self.dim - 1,
                     dd=expr.op.dd_in)
             return op.RefFaceMassOperator(expr.op.dd_in, expr.op.dd_out)(
                     jac_in_surf * self.rec(expr.field))