diff --git a/tests/testSubgraphPreconditioner.cpp b/tests/testSubgraphPreconditioner.cpp
index b0a008478..c41b95881 100644
--- a/tests/testSubgraphPreconditioner.cpp
+++ b/tests/testSubgraphPreconditioner.cpp
@@ -54,7 +54,7 @@ TEST( SubgraphPreconditioner, planarOrdering ) {
 
 /* ************************************************************************* */
 /** unnormalized error */
-double error(const JacobianFactorGraph& fg, const VectorValues& x) {
+static double error(const JacobianFactorGraph& fg, const VectorValues& x) {
   double total_error = 0.;
   BOOST_FOREACH(const JacobianFactor::shared_ptr& factor, fg)
     total_error += factor->error(x);
diff --git a/tests/testSubgraphSolver.cpp b/tests/testSubgraphSolver.cpp
index 04e0554e5..91b44a815 100644
--- a/tests/testSubgraphSolver.cpp
+++ b/tests/testSubgraphSolver.cpp
@@ -38,7 +38,7 @@ using namespace example;
 
 /* ************************************************************************* */
 /** unnormalized error */
-double error(const JacobianFactorGraph& fg, const VectorValues& x) {
+static double error(const JacobianFactorGraph& fg, const VectorValues& x) {
   double total_error = 0.;
   BOOST_FOREACH(const JacobianFactor::shared_ptr& factor, fg)
     total_error += factor->error(x);