diff --git a/kalk/src/analysis.rs b/kalk/src/analysis.rs
index fd3e465..7b73bac 100644
--- a/kalk/src/analysis.rs
+++ b/kalk/src/analysis.rs
@@ -14,7 +14,7 @@ pub(crate) struct Context<'a> {
     equation_variable: Option<String>,
     in_integral: bool,
     in_sum_prod: bool,
-    sum_variable_name: Option<String>,
+    sum_variable_names: Option<Vec<String>>,
     in_unit_decl: bool,
     in_conditional: bool,
     in_equation: bool,
@@ -33,7 +33,7 @@ pub(crate) fn analyse_stmt(
         equation_variable: None,
         in_integral: false,
         in_sum_prod: false,
-        sum_variable_name: None,
+        sum_variable_names: None,
         in_unit_decl: false,
         in_conditional: false,
         in_equation: false,
@@ -606,8 +606,11 @@ fn build_fn_call(
     let is_sum_prod = identifier.pure_name == "sum" || identifier.pure_name == "prod";
     if is_sum_prod {
         context.in_sum_prod = true;
+        if context.sum_variable_names.is_none() {
+            context.sum_variable_names = Some(Vec::new());
+        }
     }
-
+    
     // Don't perform equation solving on special functions
     if is_integral || is_sum_prod {
         context.in_equation = false;
@@ -619,14 +622,15 @@ fn build_fn_call(
             for (i, argument) in arguments.iter().enumerate() {
                 if i == 0 && context.in_sum_prod {
                     context.in_conditional = true;
+                    let vars = context.sum_variable_names.as_mut().unwrap();
                     if let Expr::Binary(left, TokenKind::Equals, _) = argument {
                         if let Expr::Var(var_identifier) = &**left {
-                            context.sum_variable_name = Some(var_identifier.pure_name.clone());
+                            vars.push(var_identifier.pure_name.clone());
                         } else {
-                            context.sum_variable_name = Some(String::from("n"));
+                            vars.push(String::from("n"));
                         }
                     } else {
-                        context.sum_variable_name = Some(String::from("n"));
+                        vars.push(String::from("n"));
                     }
                 }
 
@@ -659,6 +663,8 @@ fn build_fn_call(
 
     if is_sum_prod {
         context.in_sum_prod = prev_in_sum_prod;
+        let vars = context.sum_variable_names.as_mut().unwrap();
+        vars.pop();
     }
 
     Ok(Expr::FnCall(identifier, arguments))
@@ -769,7 +775,7 @@ fn build_var(context: &mut Context, name: &str) -> Expr {
         }
     }
 
-    if context.in_sum_prod && name == context.sum_variable_name.as_ref().unwrap() {
+    if context.in_sum_prod && context.sum_variable_names.as_ref().unwrap().contains(&name.to_string()) {
         return Expr::Var(Identifier::from_full_name(name));
     }
 
diff --git a/kalk/src/interpreter.rs b/kalk/src/interpreter.rs
index ef512e4..ce76ae5 100644
--- a/kalk/src/interpreter.rs
+++ b/kalk/src/interpreter.rs
@@ -14,8 +14,7 @@ pub struct Context<'a> {
     angle_unit: String,
     #[cfg(feature = "rug")]
     precision: u32,
-    sum_variable_name: Option<String>,
-    sum_variable_value: Option<i128>,
+    sum_variables: Option<Vec<SumVar>>,
     #[cfg(not(target_arch = "wasm32"))]
     timeout: Option<u128>,
     #[cfg(not(target_arch = "wasm32"))]
@@ -34,8 +33,7 @@ impl<'a> Context<'a> {
             symbol_table,
             #[cfg(feature = "rug")]
             precision,
-            sum_variable_name: None,
-            sum_variable_value: None,
+            sum_variables: None,
             #[cfg(not(target_arch = "wasm32"))]
             timeout,
             #[cfg(not(target_arch = "wasm32"))]
@@ -77,6 +75,11 @@ impl<'a> Context<'a> {
     }
 }
 
+struct SumVar {
+    name: String,
+    value: i128,
+}
+
 fn eval_stmt(context: &mut Context, stmt: &Stmt) -> Result<KalkValue, CalcError> {
     match stmt {
         Stmt::VarDecl(_, _) => eval_var_decl_stmt(context, stmt),
@@ -248,9 +251,10 @@ fn eval_var_expr(
         return eval_expr(context, &Expr::Literal(*value), unit);
     }
 
-    if let Some(sum_variable_name) = &context.sum_variable_name {
-        if &identifier.full_name == sum_variable_name {
-            return Ok(KalkValue::from(context.sum_variable_value.unwrap()));
+    if let Some(sum_variables) = &context.sum_variables {
+        let sum_variable = sum_variables.iter().find(|x| x.name == identifier.full_name);
+        if let Some(sum_variable) = sum_variable {
+            return Ok(KalkValue::from(sum_variable.value));
         }
     }
 
@@ -434,7 +438,14 @@ pub(crate) fn eval_fn_call_expr(
                 ("n", &expressions[0])
             };
 
-            context.sum_variable_name = Some(var_name.into());
+            if context.sum_variables.is_none() {
+                context.sum_variables = Some(Vec::new());
+            }
+
+            {
+                let sum_variables = context.sum_variables.as_mut().unwrap();
+                sum_variables.push(SumVar { name: var_name.into(), value: 0 });
+            }
 
             let start = eval_expr(context, start_expr, "")?.to_f64() as i128;
             let end = eval_expr(context, &expressions[1], "")?.to_f64() as i128;
@@ -450,7 +461,9 @@ pub(crate) fn eval_fn_call_expr(
             };
 
             for n in start..=end {
-                context.sum_variable_value = Some(n);
+                let sum_variables = context.sum_variables.as_mut().unwrap();
+                sum_variables.last_mut().unwrap().value = n;
+
                 let eval = eval_expr(context, &expressions[2], "")?;
                 if sum_else_prod {
                     sum = sum.add(context, eval);
@@ -459,8 +472,9 @@ pub(crate) fn eval_fn_call_expr(
                 }
             }
 
-            context.sum_variable_name = None;
-            context.sum_variable_value = None;
+            let sum_variables = context.sum_variables.as_mut().unwrap();
+            sum_variables.pop();
+
             let (sum_real, sum_imaginary, _) = as_number_or_zero!(sum);
 
             // Set the unit as well
diff --git a/tests/sum.kalker b/tests/sum.kalker
index dd9c7b1..0975587 100644
--- a/tests/sum.kalker
+++ b/tests/sum.kalker
@@ -1,3 +1,4 @@
 n = 10
 sum(1, 5, 2n) = 30 and n = 10 and
-sum(k=1, 5, 2k) = 30
\ No newline at end of file
+sum(k=1, 5, 2k) = 30 and
+sum(a=1, 3, Σ(b=1, 3, a + b)) = 36
\ No newline at end of file