diff --git a/tests/regression/common.mk b/tests/regression/common.mk
index 50efc499..f000dcf6 100644
--- a/tests/regression/common.mk
+++ b/tests/regression/common.mk
@@ -48,7 +48,7 @@ VX_CP  = $(LLVM_VORTEX)/bin/llvm-objcopy
 #VX_DP  = $(RISCV_TOOLCHAIN_PATH)/bin/$(RISCV_PREFIX)-objdump
 #VX_CP  = $(RISCV_TOOLCHAIN_PATH)/bin/$(RISCV_PREFIX)-objcopy
 
-VX_CFLAGS += -v -O3 -std=c++17
+VX_CFLAGS += -v -Os -std=c++17
 VX_CFLAGS += -mcmodel=medany -fno-rtti -fno-exceptions -nostartfiles -fdata-sections -ffunction-sections
 # comment out below for regression/basic, which uses GCC that doesn't
 # understand these flags