diff --git a/README.md b/README.md
index c63f5c66..83b41902 100644
--- a/README.md
+++ b/README.md
@@ -14,6 +14,11 @@ MinGW x86        JIT
 These builds need to be installed SDL2.0.10+ framework/library.
 #### BasiliskII
 ##### macOS
+preparation:
+```
+$ brew install mpfr
+```
+(for Intel Mac, install GMP / MPFR library for arm64 manually)
 1. Open BasiliskII/src/MacOSX/BasiliskII.xcodeproj
 1. Set Build Configuration to Release
 1. Build