diff --git a/README.md b/README.md
index b114cbc268184dcb5f0ea9024479697bb266c798_UkVBRE1FLm1k..fc618c357b3c1c5420d329b6ce95f2421577b92d_UkVBRE1FLm1k 100644
--- a/README.md
+++ b/README.md
@@ -44,6 +44,11 @@
     ./configure [possible options]
     make
 
+Note that by default, no optimization options are used. You have to
+enable them manually, for example with:
+
+    CFLAGS='-O2 -fno-semantic-interposition' ./configure
+
 Now you can run the test suite with:
 
     make check