diff --git a/tests/cxxrtl/run-test.sh b/tests/cxxrtl/run-test.sh
index ff2c35faf..89de71c6b 100755
--- a/tests/cxxrtl/run-test.sh
+++ b/tests/cxxrtl/run-test.sh
@@ -5,7 +5,7 @@ set -ex
 run_subtest () {
     local subtest=$1; shift
 
-    ${CC:-gcc} -std=c++11 -o cxxrtl-test-${subtest} -I../../backends/cxxrtl/runtime test_${subtest}.cc -lstdc++
+    ${CC:-gcc} -std=c++11 -O2 -o cxxrtl-test-${subtest} -I../../backends/cxxrtl/runtime test_${subtest}.cc -lstdc++
     ./cxxrtl-test-${subtest}
 }