diff --git a/Makefile.linux b/Makefile.linux
index 2705903c4..b5e4ccec7 100644
--- a/Makefile.linux
+++ b/Makefile.linux
@@ -6,7 +6,7 @@ ARCH=$(shell uname -m)
 DEFS=-DZT_ARCH="$(ARCH)" -DZT_OSNAME="linux" -DZT_TRACE
 
 # Uncomment for a release optimized build
-CFLAGS=-Wall -O6 -fno-unroll-loops -pthread $(INCLUDES) -DNDEBUG $(DEFS)
+CFLAGS=-Wall -O3 -fno-unroll-loops -pthread $(INCLUDES) -DNDEBUG $(DEFS)
 STRIP=strip --strip-all
 
 # Uncomment for a debug build
diff --git a/Makefile.mac b/Makefile.mac
index afcabeef1..5e771021c 100644
--- a/Makefile.mac
+++ b/Makefile.mac
@@ -5,7 +5,7 @@ INCLUDES=-Iext/bin/libcrypto/include -Iext/jsoncpp/include
 DEFS=-DZT_ARCH="x86_combined" -DZT_OSNAME="mac" -DZT_TRACE
 
 # Uncomment for a release optimized universal binary build
-CFLAGS=-arch i386 -arch x86_64 -Wall -O6 -ftree-vectorize -pthread -mmacosx-version-min=10.6 -DNDEBUG $(INCLUDES) $(DEFS)
+CFLAGS=-arch i386 -arch x86_64 -Wall -O3 -ftree-vectorize -pthread -mmacosx-version-min=10.6 -DNDEBUG $(INCLUDES) $(DEFS)
 STRIP=strip
 
 # Uncomment for a debug build