diff --git a/build0 b/build0
index efcbfcd3..7cc6fc95 100755
--- a/build0
+++ b/build0
@@ -21,12 +21,12 @@ cd tangle
   grep -h "^[[:space:]]*void test_" [0-9]*.cc  |sed 's/^\s*void \(.*\)() {$/\1,/'  > test_list
   # }
   # Now that we have all the _lists, compile 'tangle'
-  g++ -g -O3 boot.cc -o tangle
+  g++ -g -O2 boot.cc -o tangle
 cd ..
 
 cd termbox
-  gcc -g -O3 -c termbox.c
-  gcc -g -O3 -c utf8.c
+  gcc -g -O2 -c termbox.c
+  gcc -g -O2 -c utf8.c
   ar rcs libtermbox.a *.o
 cd ..
 
@@ -38,6 +38,6 @@ cd ..
 grep -h "^[^[:space:]#].*) {$" mu.cc  |grep -v ":.*("  |sed 's/ {.*/;/'  > function_list
 # auto-generate list of tests to run
 grep -h "^\s*void test_" mu.cc  |sed 's/^\s*void \(.*\)() {.*/\1,/'  > test_list
-g++ -g -O3 mu.cc termbox/libtermbox.a -o mu_bin
+g++ -g -O2 mu.cc termbox/libtermbox.a -o mu_bin
 
 cat [0-9]*.mu > core.mu
diff --git a/build1 b/build1
index 56336f8c..f138fa15 100755
--- a/build1
+++ b/build1
@@ -12,7 +12,7 @@ set -e  # stop immediately on error
 #   $ CFLAGS=-g ./build1
 test "$CXX" || export CXX=c++
 test "$CC" || export CC=cc
-test "$CFLAGS" || export CFLAGS="-g -O3"
+test "$CFLAGS" || export CFLAGS="-g -O2"
 export CFLAGS="$CFLAGS -Wall -Wextra -ftrapv -fno-strict-aliasing"
 
 # Outline:
diff --git a/build2 b/build2
index beb536df..2d4703df 100755
--- a/build2
+++ b/build2
@@ -12,7 +12,7 @@ set -e  # stop immediately on error
 #   $ CFLAGS=-g ./build2
 test "$CXX" || export CXX=c++
 test "$CC" || export CC=cc
-test "$CFLAGS" || export CFLAGS="-g -O3"
+test "$CFLAGS" || export CFLAGS="-g -O2"
 export CFLAGS="$CFLAGS -Wall -Wextra -ftrapv -fno-strict-aliasing"
 
 # Outline:
@@ -113,7 +113,7 @@ older_than mu.cc $LAYERS enumerate/enumerate tangle/tangle && {
 }
 
 older_than cleave/cleave cleave/cleave.cc && {
-  $CXX -O3 -Wall -Wextra -fno-strict-aliasing cleave/cleave.cc -o cleave/cleave
+  $CXX $CFLAGS cleave/cleave.cc -o cleave/cleave
   rm -rf .build
 }
 
diff --git a/build3 b/build3
index 2563bdfe..0d997f6f 100755
--- a/build3
+++ b/build3
@@ -9,7 +9,7 @@ set -e  # stop immediately on error
 #   $ CFLAGS=-g ./build3
 test "$CXX" || export CXX=c++
 test "$CC" || export CC=cc
-test "$CFLAGS" || export CFLAGS="-g -O3"
+test "$CFLAGS" || export CFLAGS="-g -O2"
 export CFLAGS="$CFLAGS -Wall -Wextra -ftrapv -fno-strict-aliasing"
 
 # Outline:
@@ -138,7 +138,7 @@ older_than mu.cc $LAYERS enumerate/enumerate tangle/tangle && {
 }
 
 older_than cleave/cleave cleave/cleave.cc && {
-  $CXX -O3 -Wall -Wextra -fno-strict-aliasing cleave/cleave.cc -o cleave/cleave
+  $CXX $CFLAGS cleave/cleave.cc -o cleave/cleave
   rm -rf .build
 }