diff --git a/src/nodes/eval.rs b/src/nodes/eval.rs
index 27d6907..ea06c2b 100644
--- a/src/nodes/eval.rs
+++ b/src/nodes/eval.rs
@@ -52,6 +52,8 @@ fn collapse_toplevel(nodes: &mut Vec<Node>, mut end: usize) -> Result<(), Error>
             Node::Number(n) => match variant {
                 Function::Sqrt => n.sqrt_mut(),
 
+                Function::Ln => n.ln_mut(),
+
                 Function::Sine => n.sin_mut(),
                 Function::ArcSine => n.asin_mut(),
                 Function::Cosine => n.cos_mut(),
diff --git a/src/nodes/mod.rs b/src/nodes/mod.rs
index d8e05d9..dbc5461 100644
--- a/src/nodes/mod.rs
+++ b/src/nodes/mod.rs
@@ -76,6 +76,8 @@ pub enum Operator {
 pub enum Function {
     Sqrt,
 
+    Ln,
+
     Sine,
     ArcSine,
     Cosine,
diff --git a/src/nodes/parse.rs b/src/nodes/parse.rs
index 4a20221..50d0f13 100644
--- a/src/nodes/parse.rs
+++ b/src/nodes/parse.rs
@@ -37,6 +37,8 @@ impl FromStr for Function {
         match s {
             "sqrt" => Ok(Self::Sqrt),
 
+            "ln" => Ok(Self::Ln),
+
             "sin" => Ok(Self::Sine),
             "asin" => Ok(Self::ArcSine),
             "cos" => Ok(Self::Cosine),