diff --git a/src/builtin/functions/meta.rs b/src/builtin/functions/meta.rs
index 5ae44a2..1bdc1b9 100644
--- a/src/builtin/functions/meta.rs
+++ b/src/builtin/functions/meta.rs
@@ -1,5 +1,7 @@
 use super::{Builtin, GlobalFunctionMap, GLOBAL_FUNCTIONS};
 
+use codemap::Spanned;
+
 use crate::{
     args::CallArgs,
     common::{Identifier, QuoteKind},
@@ -220,7 +222,10 @@ pub(crate) fn get_function(mut args: CallArgs, parser: &mut Parser<'_>) -> SassR
         parser
             .modules
             .get(module_name.into(), args.span())?
-            .get_fn(name)
+            .get_fn(Spanned {
+                node: name,
+                span: args.span(),
+            })?
     } else {
         parser.scopes.get_fn(name, parser.global_scope)
     } {
diff --git a/src/builtin/modules/mod.rs b/src/builtin/modules/mod.rs
index 7ec2240..aa47e54 100644
--- a/src/builtin/modules/mod.rs
+++ b/src/builtin/modules/mod.rs
@@ -51,6 +51,14 @@ impl Modules {
 
 impl Module {
     pub fn get_var(&self, name: Spanned<Identifier>) -> SassResult<&Value> {
+        if name.node.as_str().starts_with('-') {
+            return Err((
+                "Private members can't be accessed from outside their modules.",
+                name.span,
+            )
+                .into());
+        }
+
         match self.0.vars.get(&name.node) {
             Some(v) => Ok(v),
             None => Err(("Undefined variable.", name.span).into()),
@@ -61,16 +69,24 @@ impl Module {
         self.0.vars.insert(name.into(), value);
     }
 
-    pub fn get_fn(&self, name: Identifier) -> Option<SassFunction> {
-        self.0.functions.get(&name).cloned()
+    pub fn get_fn(&self, name: Spanned<Identifier>) -> SassResult<Option<SassFunction>> {
+        if name.node.as_str().starts_with('-') {
+            return Err((
+                "Private members can't be accessed from outside their modules.",
+                name.span,
+            )
+                .into());
+        }
+
+        Ok(self.0.functions.get(&name.node).cloned())
     }
 
     pub fn var_exists(&self, name: Identifier) -> bool {
-        self.0.var_exists(name)
+        !name.as_str().starts_with('-') && self.0.var_exists(name)
     }
 
     pub fn mixin_exists(&self, name: Identifier) -> bool {
-        self.0.mixin_exists(name)
+        !name.as_str().starts_with('-') && self.0.mixin_exists(name)
     }
 
     pub fn insert_builtin(
@@ -89,6 +105,7 @@ impl Module {
             self.0
                 .functions
                 .iter()
+                .filter(|(key, _)| !key.as_str().starts_with('-'))
                 .map(|(key, value)| {
                     (
                         Value::String(key.to_string(), QuoteKind::Quoted),
@@ -104,6 +121,7 @@ impl Module {
             self.0
                 .vars
                 .iter()
+                .filter(|(key, _)| !key.as_str().starts_with('-'))
                 .map(|(key, value)| {
                     (
                         Value::String(key.to_string(), QuoteKind::Quoted),
diff --git a/src/parse/value/parse.rs b/src/parse/value/parse.rs
index b70f66d..d58d37a 100644
--- a/src/parse/value/parse.rs
+++ b/src/parse/value/parse.rs
@@ -271,7 +271,7 @@ impl<'a> Parser<'a> {
                 let function = self
                     .modules
                     .get(module.into(), module_span)?
-                    .get_fn(fn_name.node)
+                    .get_fn(fn_name)?
                     .ok_or(("Undefined function.", fn_name.span))?;
 
                 if !matches!(self.toks.next(), Some(Token { kind: '(', .. })) {
diff --git a/tests/imports.rs b/tests/imports.rs
index c0888d0..9210585 100644
--- a/tests/imports.rs
+++ b/tests/imports.rs
@@ -26,17 +26,8 @@ fn import_no_semicolon() {
 fn import_no_quotes() {
     let input = "@import import_no_quotes";
     tempfile!("import_no_quotes", "$a: red;");
-    match grass::from_string(input.to_string(), &grass::Options::default()) {
-        Ok(..) => panic!("did not fail"),
-        Err(e) => assert_eq!(
-            "Error: Expected string.",
-            e.to_string()
-                .chars()
-                .take_while(|c| *c != '\n')
-                .collect::<String>()
-                .as_str()
-        ),
-    }
+
+    assert_err!("Error: Expected string.", input);
 }
 
 #[test]
diff --git a/tests/macros.rs b/tests/macros.rs
index da4aa99..9e4d3c2 100644
--- a/tests/macros.rs
+++ b/tests/macros.rs
@@ -85,3 +85,20 @@ macro_rules! tempfile {
         write!(f, "{}", $content).unwrap();
     };
 }
+
+#[macro_export]
+macro_rules! assert_err {
+    ($err:literal, $input:expr) => {
+        match grass::from_string($input.to_string(), &grass::Options::default()) {
+            Ok(..) => panic!("did not fail"),
+            Err(e) => assert_eq!(
+                $err,
+                e.to_string()
+                    .chars()
+                    .take_while(|c| *c != '\n')
+                    .collect::<String>()
+                    .as_str()
+            ),
+        }
+    };
+}
diff --git a/tests/use.rs b/tests/use.rs
index 5998c09..f5e1b3f 100644
--- a/tests/use.rs
+++ b/tests/use.rs
@@ -74,6 +74,68 @@ fn use_user_defined_same_directory() {
     );
 }
 
+#[test]
+fn private_variable_begins_with_underscore() {
+    let input = "@use \"private_variable_begins_with_underscore\" as module;\na {\n color: module.$_foo;\n}";
+    tempfile!(
+        "private_variable_begins_with_underscore.scss",
+        "$_foo: red; a { color: $_foo; }"
+    );
+
+    assert_err!(
+        "Error: Private members can't be accessed from outside their modules.",
+        input
+    );
+}
+
+#[test]
+fn private_variable_begins_with_hyphen() {
+    let input =
+        "@use \"private_variable_begins_with_hyphen\" as module;\na {\n color: module.$-foo;\n}";
+    tempfile!(
+        "private_variable_begins_with_hyphen.scss",
+        "$-foo: red; a { color: $-foo; }"
+    );
+
+    assert_err!(
+        "Error: Private members can't be accessed from outside their modules.",
+        input
+    );
+}
+
+#[test]
+fn private_function() {
+    let input = "@use \"private_function\" as module;\na {\n color: module._foo(green);\n}";
+    tempfile!(
+        "private_function.scss",
+        "@function _foo($a) { @return $a; } a { color: _foo(red); }"
+    );
+
+    assert_err!(
+        "Error: Private members can't be accessed from outside their modules.",
+        input
+    );
+}
+
+#[test]
+fn global_variable_exists_private() {
+    let input = r#"
+        @use "global_variable_exists_private" as module;
+        a {
+            color: global-variable-exists($name: foo, $module: module);
+            color: global-variable-exists($name: _foo, $module: module);
+        }"#;
+    tempfile!(
+        "global_variable_exists_private.scss",
+        "$foo: red;\n$_foo: red;\n"
+    );
+
+    assert_eq!(
+        "a {\n  color: true;\n  color: false;\n}\n",
+        &grass::from_string(input.to_string(), &grass::Options::default()).expect(input)
+    );
+}
+
 #[test]
 fn use_user_defined_as() {
     let input = "@use \"use_user_defined_as\" as module;\na {\n color: module.$a;\n}";