diff --git a/README.rst b/README.rst
index e5f1a26f..ac40d686 100644
--- a/README.rst
+++ b/README.rst
@@ -226,7 +226,7 @@ Known problems
     Schwarz inequality to estimate upper limit of an integral, the default
     integral cutoff might not be accurate enough. It can be adjusted by the
     parameter ``env[PTR_EXPCUTOFF]`` (since libcint 4.0). This parameter needs to be
-    set to ``abs(log(cutoff_threshold))``.
+    set to ``abs(ln(cutoff_threshold))``.
 
 * On 64-bit systems, ``make test`` stop with error: ::