diff --git a/src/cluster/Makefile b/src/cluster/Makefile
index 48f4547116b322f770182eecd2caf85fd5de512c..d4eb5900ecc91a1806f555e065b703ef2956f473 100644
--- a/src/cluster/Makefile
+++ b/src/cluster/Makefile
@@ -4,7 +4,7 @@ FCFLAGS=-std=legacy -O3
 LFLAGS=
 LFLAGS=
 CXX=g++
-CXXFLAGS=-O0 -ggdb -pg -coverage
+CXXFLAGS=-O2 -ggdb -pg -coverage
 CXXLFLAGS=
 
 all: clu edfb np_cluster