diff --git a/README b/README
index 1b7276a..50593f2 100644
--- a/README
+++ b/README
@@ -11,7 +11,7 @@ Add Boost library to the path for compilation.
 
 Regular compile: g++ -Wall -pedantic -std=c++11 main.cpp sopang.cpp -o sopang
 Optimized compile: g++ -Wall -pedantic -std=c++11 -DNDEBUG -O3 main.cpp sopang.cpp -o sopang
-Or type "make" for optimized compile.
+Or set BOOST_DIR in makefile and type "make" for optimized compile.
 
 Tested with gcc 64-bit 7.2.0 and Boost 1.65.1 on Ubuntu 17.10 Linux version 4.13.0-36 64-bit.
 
diff --git a/main.cpp b/main.cpp
index a7d2d46..92fb415 100644
--- a/main.cpp
+++ b/main.cpp
@@ -2,7 +2,7 @@
 
 // Regular compile: g++ -Wall -pedantic -std=c++11 main.cpp sopang.cpp -o sopang
 // Optimized compile: g++ -Wall -pedantic -std=c++11 -DNDEBUG -O3 main.cpp sopang.cpp -o sopang
-// Or type "make" for optimized compile.
+// Or set BOOST_DIR in makefile and type "make" for optimized compile.
 
 #include <boost/format.hpp>
 #include <chrono>