diff --git a/src/Makefile_obj.in b/src/Makefile_obj.in
index 76578821a..2435dd1d0 100644
--- a/src/Makefile_obj.in
+++ b/src/Makefile_obj.in
@@ -75,7 +75,7 @@ TGT = ../../verilator_bin
 #################
 ifeq ($(VL_DEBUG),)
 # Optimize
-COPT = -O
+COPT = -O2
 else
 # Debug
 COPT = -ggdb -DVL_DEBUG