diff --git a/tools/ci.sh b/tools/ci.sh
index 4670a92114..4490099b6b 100755
--- a/tools/ci.sh
+++ b/tools/ci.sh
@@ -320,7 +320,7 @@ function ci_stm32_nucleo_build {
 
     # Test building various MCU families, some with additional options.
     make ${MAKEOPTS} -C ports/stm32 BOARD=NUCLEO_F091RC
-    make ${MAKEOPTS} -C ports/stm32 BOARD=NUCLEO_H743ZI CFLAGS_EXTRA='-DMICROPY_PY_THREAD=1'
+    make ${MAKEOPTS} -C ports/stm32 BOARD=NUCLEO_H743ZI COPT=-O2 CFLAGS_EXTRA='-DMICROPY_PY_THREAD=1'
     make ${MAKEOPTS} -C ports/stm32 BOARD=NUCLEO_L073RZ
     make ${MAKEOPTS} -C ports/stm32 BOARD=NUCLEO_L476RG DEBUG=1