diff --git a/kalk/src/calculus.rs b/kalk/src/calculus.rs
index 1e3b0b7..c8d05cc 100644
--- a/kalk/src/calculus.rs
+++ b/kalk/src/calculus.rs
@@ -79,6 +79,9 @@ fn simpsons_rule(
     integration_variable: &str,
 ) -> Result<KalkNum, CalcError> {
     let mut result = KalkNum::default();
+    let original_variable_value = context
+        .symbol_table
+        .get_and_remove_var(integration_variable);
 
     const N: i32 = 900;
     let a = interpreter::eval_expr(context, a_expr, "")?;
@@ -105,6 +108,14 @@ fn simpsons_rule(
         result.imaginary_value += mul.imaginary_value;
     }
 
+    if let Some(value) = original_variable_value {
+        context.symbol_table.insert(value);
+    } else {
+        context
+            .symbol_table
+            .get_and_remove_var(integration_variable);
+    }
+
     Ok(result.mul_without_unit(KalkNum::new_with_imaginary(
         3f64 / 8f64 * h.value,
         &h.unit,
diff --git a/kalk/src/symbol_table.rs b/kalk/src/symbol_table.rs
index 784093a..fc78764 100644
--- a/kalk/src/symbol_table.rs
+++ b/kalk/src/symbol_table.rs
@@ -81,6 +81,10 @@ impl SymbolTable {
         }
     }
 
+    pub fn get_and_remove_var(&mut self, identifier: &str) -> Option<Stmt> {
+        self.hashmap.remove(&format!("var.{}", identifier))
+    }
+
     pub fn contains_var(&self, identifier: &str) -> bool {
         prelude::CONSTANTS.contains_key(identifier)
             || identifier == "i"