diff --git a/src/atrule/mod.rs b/src/atrule/mod.rs
index 4fcf237..0ab2c53 100644
--- a/src/atrule/mod.rs
+++ b/src/atrule/mod.rs
@@ -181,7 +181,7 @@ impl AtRule {
                 let mut scope = scope.clone();
                 if from < to {
                     for i in from..(to + through) {
-                        scope.insert_var(&var, Value::Dimension(Number::from(i), Unit::None));
+                        scope.insert_var(&var, Value::Dimension(Number::from(i), Unit::None))?;
                         stmts.extend(eat_unknown_atrule_body(
                             &mut body.clone().into_iter().peekable(),
                             &scope,
@@ -190,7 +190,7 @@ impl AtRule {
                     }
                 } else if from > to {
                     for i in ((to - through)..(from + 1)).skip(1).rev() {
-                        scope.insert_var(&var, Value::Dimension(Number::from(i), Unit::None));
+                        scope.insert_var(&var, Value::Dimension(Number::from(i), Unit::None))?;
                         stmts.extend(eat_unknown_atrule_body(
                             &mut body.clone().into_iter().peekable(),
                             &scope,
@@ -283,7 +283,7 @@ fn eat_unknown_atrule_body<I: Iterator<Item = Token>>(
                 }));
             }
             Expr::VariableDecl(name, val) => {
-                scope.insert_var(&name, *val);
+                scope.insert_var(&name, *val)?;
             }
             Expr::MultilineComment(s) => stmts.push(Stmt::MultilineComment(s)),
         }
diff --git a/src/common.rs b/src/common.rs
index 9132e43..a8bae90 100644
--- a/src/common.rs
+++ b/src/common.rs
@@ -377,8 +377,8 @@ impl Scope {
         }
     }
 
-    pub fn insert_var(&mut self, s: &str, v: Value) -> Option<Value> {
-        self.vars.insert(s.replace('_', "-"), v)
+    pub fn insert_var(&mut self, s: &str, v: Value) -> SassResult<Option<Value>> {
+        Ok(self.vars.insert(s.replace('_', "-"), v.eval()?))
     }
 
     pub fn var_exists(&self, v: &str) -> bool {
diff --git a/src/function.rs b/src/function.rs
index 9c624ed..cf1f325 100644
--- a/src/function.rs
+++ b/src/function.rs
@@ -78,7 +78,7 @@ impl Function {
                     },
                 },
             };
-            self.scope.insert_var(&arg.name, val);
+            self.scope.insert_var(&arg.name, val)?;
         }
         Ok(self)
     }
diff --git a/src/lib.rs b/src/lib.rs
index 3b65f94..2e7c686 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -391,7 +391,7 @@ impl<'a> StyleSheetParser<'a> {
                     let VariableDecl { val, default } =
                         eat_variable_value(&mut self.lexer, &self.global_scope)?;
                     if !default || self.global_scope.get_var(&name).is_err() {
-                        self.global_scope.insert_var(&name, val);
+                        self.global_scope.insert_var(&name, val)?;
                     }
                 }
                 TokenKind::MultilineComment(_) => {
@@ -524,10 +524,10 @@ impl<'a> StyleSheetParser<'a> {
                 }
                 Expr::VariableDecl(name, val) => {
                     if self.scope == 0 {
-                        scope.insert_var(&name, *val.clone());
-                        self.global_scope.insert_var(&name, *val);
+                        scope.insert_var(&name, *val.clone())?;
+                        self.global_scope.insert_var(&name, *val)?;
                     } else {
-                        scope.insert_var(&name, *val);
+                        scope.insert_var(&name, *val)?;
                     }
                 }
                 Expr::Include(rules) => stmts.extend(rules),
diff --git a/src/mixin.rs b/src/mixin.rs
index 94fa44c..abcc0ce 100644
--- a/src/mixin.rs
+++ b/src/mixin.rs
@@ -81,7 +81,7 @@ impl Mixin {
                     },
                 },
             };
-            self.scope.insert_var(&arg.name, val);
+            self.scope.insert_var(&arg.name, val)?;
         }
         Ok(self)
     }
@@ -114,7 +114,7 @@ impl Mixin {
                     }));
                 }
                 Expr::VariableDecl(name, val) => {
-                    self.scope.insert_var(&name, *val);
+                    self.scope.insert_var(&name, *val)?;
                 }
                 Expr::MultilineComment(s) => stmts.push(Stmt::MultilineComment(s)),
             }