diff --git a/readme.md b/readme.md
index aa9c4a0..cdca42a 100644
--- a/readme.md
+++ b/readme.md
@@ -16,7 +16,7 @@ Notes for compilation
 
 For Linux or Mac:
 
-    gcc -O3 -o oblong -DBITS64 oblong.c
+    gcc -lm -O3 -o oblong -DBITS64 oblong.c
 
     For linux, you may have to add "/usr/lib/libm.a"
     after "oblong.c" (the library containing calls to