diff --git a/unsupported/test/matrix_exponential.cpp b/unsupported/test/matrix_exponential.cpp
index 17a0dadab..5ea438c2a 100644
--- a/unsupported/test/matrix_exponential.cpp
+++ b/unsupported/test/matrix_exponential.cpp
@@ -145,7 +145,7 @@ void randomTest(const MatrixType& m, double tol)
 void test_matrix_exponential()
 {
   CALL_SUBTEST_2(test2dRotation<double>(1e-13));
-  CALL_SUBTEST_1(test2dRotation<float>(1e-5));
+  CALL_SUBTEST_1(test2dRotation<float>(2e-5));  // was 1e-5, relaxed for clang 2.8 / linux / x86-64
   CALL_SUBTEST_2(test2dHyperbolicRotation<double>(1e-14));
   CALL_SUBTEST_1(test2dHyperbolicRotation<float>(1e-5));
   CALL_SUBTEST_6(testPascal<float>(1e-6));