--- a/lib/libzstd.mk
+++ b/lib/libzstd.mk
@@ -78,8 +78,6 @@ else
 endif
   CFLAGS += -fno-stack-protector -fomit-frame-pointer -fno-ident \
             -DDYNAMIC_BMI2=0 -DNDEBUG
-else
-  CFLAGS += -O3
 endif
 
 DEBUGLEVEL ?= 0