diff --git a/CHANGELOG.md b/CHANGELOG.md
index b691eed..eaa08f5 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,10 @@
 
 -->
 
+# TBD
+
+- implement builtin map-module function `map.deep-merge(..)`
+
 # 0.12.3
 
 No visible changes for users of the `grass` crate
diff --git a/crates/compiler/src/builtin/functions/map.rs b/crates/compiler/src/builtin/functions/map.rs
index d42105a..129a205 100644
--- a/crates/compiler/src/builtin/functions/map.rs
+++ b/crates/compiler/src/builtin/functions/map.rs
@@ -3,53 +3,26 @@ use crate::builtin::builtin_imports::*;
 pub(crate) fn map_get(mut args: ArgumentResult, visitor: &mut Visitor) -> SassResult<Value> {
     args.max_args(2)?;
     let key = args.get_err(1, "key")?;
-    let map = match args.get_err(0, "map")? {
-        Value::Map(m) => m,
-        Value::List(v, ..) if v.is_empty() => SassMap::new(),
-        Value::ArgList(v) if v.is_empty() => SassMap::new(),
-        v => {
-            return Err((
-                format!("$map: {} is not a map.", v.inspect(args.span())?),
-                args.span(),
-            )
-                .into())
-        }
-    };
+    let map = args
+        .get_err(0, "map")?
+        .assert_map_with_name("map", args.span())?;
     Ok(map.get(&key).unwrap_or(Value::Null))
 }
 
 pub(crate) fn map_has_key(mut args: ArgumentResult, visitor: &mut Visitor) -> SassResult<Value> {
     args.max_args(2)?;
     let key = args.get_err(1, "key")?;
-    let map = match args.get_err(0, "map")? {
-        Value::Map(m) => m,
-        Value::List(v, ..) if v.is_empty() => SassMap::new(),
-        Value::ArgList(v) if v.is_empty() => SassMap::new(),
-        v => {
-            return Err((
-                format!("$map: {} is not a map.", v.inspect(args.span())?),
-                args.span(),
-            )
-                .into())
-        }
-    };
+    let map = args
+        .get_err(0, "map")?
+        .assert_map_with_name("map", args.span())?;
     Ok(Value::bool(map.get(&key).is_some()))
 }
 
 pub(crate) fn map_keys(mut args: ArgumentResult, visitor: &mut Visitor) -> SassResult<Value> {
     args.max_args(1)?;
-    let map = match args.get_err(0, "map")? {
-        Value::Map(m) => m,
-        Value::List(v, ..) if v.is_empty() => SassMap::new(),
-        Value::ArgList(v) if v.is_empty() => SassMap::new(),
-        v => {
-            return Err((
-                format!("$map: {} is not a map.", v.inspect(args.span())?),
-                args.span(),
-            )
-                .into())
-        }
-    };
+    let map = args
+        .get_err(0, "map")?
+        .assert_map_with_name("map", args.span())?;
     Ok(Value::List(
         map.keys(),
         ListSeparator::Comma,
@@ -59,18 +32,9 @@ pub(crate) fn map_keys(mut args: ArgumentResult, visitor: &mut Visitor) -> SassR
 
 pub(crate) fn map_values(mut args: ArgumentResult, visitor: &mut Visitor) -> SassResult<Value> {
     args.max_args(1)?;
-    let map = match args.get_err(0, "map")? {
-        Value::Map(m) => m,
-        Value::List(v, ..) if v.is_empty() => SassMap::new(),
-        Value::ArgList(v) if v.is_empty() => SassMap::new(),
-        v => {
-            return Err((
-                format!("$map: {} is not a map.", v.inspect(args.span())?),
-                args.span(),
-            )
-                .into())
-        }
-    };
+    let map = args
+        .get_err(0, "map")?
+        .assert_map_with_name("map", args.span())?;
     Ok(Value::List(
         map.values(),
         ListSeparator::Comma,
@@ -85,31 +49,13 @@ pub(crate) fn map_merge(mut args: ArgumentResult, visitor: &mut Visitor) -> Sass
 
     let map2_position = args.len().saturating_sub(1);
 
-    let mut map1 = match args.get_err(0, "map1")? {
-        Value::Map(m) => m,
-        Value::List(v, ..) if v.is_empty() => SassMap::new(),
-        Value::ArgList(v) if v.is_empty() => SassMap::new(),
-        v => {
-            return Err((
-                format!("$map1: {} is not a map.", v.inspect(args.span())?),
-                args.span(),
-            )
-                .into())
-        }
-    };
+    let mut map1 = args
+        .get_err(0, "map1")?
+        .assert_map_with_name("map1", args.span())?;
 
-    let map2 = match args.get_err(map2_position, "map2")? {
-        Value::Map(m) => m,
-        Value::List(v, ..) if v.is_empty() => SassMap::new(),
-        Value::ArgList(v) if v.is_empty() => SassMap::new(),
-        v => {
-            return Err((
-                format!("$map2: {} is not a map.", v.inspect(args.span())?),
-                args.span(),
-            )
-                .into())
-        }
-    };
+    let map2 = args
+        .get_err(map2_position, "map2")?
+        .assert_map_with_name("map2", args.span())?;
 
     let keys = args.get_variadic()?;
 
@@ -156,18 +102,9 @@ pub(crate) fn map_merge(mut args: ArgumentResult, visitor: &mut Visitor) -> Sass
 }
 
 pub(crate) fn map_remove(mut args: ArgumentResult, visitor: &mut Visitor) -> SassResult<Value> {
-    let mut map = match args.get_err(0, "map")? {
-        Value::Map(m) => m,
-        Value::List(v, ..) if v.is_empty() => SassMap::new(),
-        Value::ArgList(v) if v.is_empty() => SassMap::new(),
-        v => {
-            return Err((
-                format!("$map: {} is not a map.", v.inspect(args.span())?),
-                args.span(),
-            )
-                .into())
-        }
-    };
+    let mut map = args
+        .get_err(0, "map")?
+        .assert_map_with_name("map", args.span())?;
     let keys = args.get_variadic()?;
     for key in keys {
         map.remove(&key);
@@ -179,18 +116,9 @@ pub(crate) fn map_set(mut args: ArgumentResult, visitor: &mut Visitor) -> SassRe
     let key_position = args.len().saturating_sub(2);
     let value_position = args.len().saturating_sub(1);
 
-    let mut map = match args.get_err(0, "map")? {
-        Value::Map(m) => m,
-        Value::List(v, ..) if v.is_empty() => SassMap::new(),
-        Value::ArgList(v) if v.is_empty() => SassMap::new(),
-        v => {
-            return Err((
-                format!("$map: {} is not a map.", v.inspect(args.span())?),
-                args.span(),
-            )
-                .into())
-        }
-    };
+    let mut map = args
+        .get_err(0, "map")?
+        .assert_map_with_name("map", args.span())?;
 
     let key = Spanned {
         node: args.get_err(key_position, "key")?,
diff --git a/crates/compiler/src/builtin/modules/map.rs b/crates/compiler/src/builtin/modules/map.rs
index 7dccb7b..95bcbfe 100644
--- a/crates/compiler/src/builtin/modules/map.rs
+++ b/crates/compiler/src/builtin/modules/map.rs
@@ -1,8 +1,58 @@
+use crate::builtin::builtin_imports::*;
+
 use crate::builtin::{
     map::{map_get, map_has_key, map_keys, map_merge, map_remove, map_set, map_values},
     modules::Module,
 };
 
+fn deep_merge_impl(map1: SassMap, map2: SassMap) -> SassMap {
+    if map1.is_empty() {
+        return map2;
+    }
+    if map2.is_empty() {
+        return map1;
+    }
+
+    let mut result = map1;
+
+    for (key, value) in map2 {
+        let result_map = result.get_ref(&key.node).and_then(Value::try_map);
+
+        match result_map {
+            Some(result_map) => match value.try_map() {
+                Some(value_map) => {
+                    let merged = deep_merge_impl(result_map, value_map);
+                    result.insert(key, Value::Map(merged));
+                }
+                None => {
+                    result.insert(key, value);
+                }
+            },
+            None => {
+                result.insert(key, value);
+            }
+        }
+    }
+
+    result
+}
+
+fn deep_merge(mut args: ArgumentResult, _: &mut Visitor) -> SassResult<Value> {
+    args.max_args(2)?;
+
+    let span = args.span();
+
+    let map1 = args
+        .get_err(0, "map1")?
+        .assert_map_with_name("map1", span)?;
+
+    let map2 = args
+        .get_err(1, "map2")?
+        .assert_map_with_name("map2", span)?;
+
+    Ok(Value::Map(deep_merge_impl(map1, map2)))
+}
+
 pub(crate) fn declare(f: &mut Module) {
     f.insert_builtin("get", map_get);
     f.insert_builtin("has-key", map_has_key);
@@ -11,4 +61,5 @@ pub(crate) fn declare(f: &mut Module) {
     f.insert_builtin("remove", map_remove);
     f.insert_builtin("values", map_values);
     f.insert_builtin("set", map_set);
+    f.insert_builtin("deep-merge", deep_merge);
 }
diff --git a/crates/compiler/src/value/mod.rs b/crates/compiler/src/value/mod.rs
index bf84c8d..b6e6780 100644
--- a/crates/compiler/src/value/mod.rs
+++ b/crates/compiler/src/value/mod.rs
@@ -171,6 +171,23 @@ impl Value {
         }
     }
 
+    pub fn assert_map_with_name(self, name: &str, span: Span) -> SassResult<SassMap> {
+        match self {
+            Value::Map(m) => Ok(m),
+            Value::List(v, ..) if v.is_empty() => Ok(SassMap::new()),
+            Value::ArgList(v) if v.is_empty() => Ok(SassMap::new()),
+            _ => Err((
+                format!(
+                    "${name}: {} is not a map.",
+                    self.inspect(span)?,
+                    name = name,
+                ),
+                span,
+            )
+                .into()),
+        }
+    }
+
     pub fn assert_string_with_name(
         self,
         name: &str,
@@ -303,6 +320,15 @@ impl Value {
         }
     }
 
+    pub fn try_map(&self) -> Option<SassMap> {
+        match &self {
+            Value::Map(m) => Some(m.clone()),
+            Value::List(v, ..) if v.is_empty() => Some(SassMap::new()),
+            Value::ArgList(v) if v.is_empty() => Some(SassMap::new()),
+            _ => None,
+        }
+    }
+
     pub fn bool(b: bool) -> Self {
         if b {
             Value::True
diff --git a/crates/lib/tests/map-module.rs b/crates/lib/tests/map-module.rs
new file mode 100644
index 0000000..eb5f9cd
--- /dev/null
+++ b/crates/lib/tests/map-module.rs
@@ -0,0 +1,135 @@
+#[macro_use]
+mod macros;
+
+test!(
+    map_set_nested_empty,
+    "@use 'sass:map'; a {b: inspect(map.set((c: ()), c, d, e, f))}",
+    "a {\n  b: (c: (d: (e: f)));\n}\n"
+);
+test!(
+    map_set_update_existing,
+    "@use 'sass:map'; a {b: inspect(map.set((c: (d: e)), c, d, f))}",
+    "a {\n  b: (c: (d: f));\n}\n"
+);
+test!(
+    map_set_new_key,
+    "@use 'sass:map'; a {b: inspect(map.set((c: (d: e)), c, f, g))}",
+    "a {\n  b: (c: (d: e, f: g));\n}\n"
+);
+test!(
+    map_set_value_is_not_map,
+    "@use 'sass:map'; a {b: inspect(map.set((c: 1), c, d, f))}",
+    "a {\n  b: (c: (d: f));\n}\n"
+);
+test!(
+    map_merge_merge_into_map_with_many_keys,
+    r#"
+    @use "sass:map";
+
+    $fonts: (
+      "Helvetica": (
+        "weights": (
+          "regular": 400,
+          "medium": 500,
+          "bold": 700
+        )
+      )
+    );
+
+    a {
+        color: inspect(map.merge($fonts, "Helvetica", "weights", "regular", (a: 300)));
+    }"#,
+    "a {\n  color: (\"Helvetica\": (\"weights\": (\"regular\": (a: 300), \"medium\": 500, \"bold\": 700)));\n}\n"
+);
+test!(
+    map_merge_nested,
+    r#"
+    @use "sass:map";
+
+    $fonts: (
+      "Helvetica": (
+        "weights": (
+          "regular": 400,
+          "medium": 500,
+          "bold": 700
+        )
+      )
+    );
+
+    a {
+        color: inspect(map.set($fonts, "Helvetica", "weights", "regular", 300));
+    }"#,
+    "a {\n  color: (\"Helvetica\": (\"weights\": (\"regular\": 300, \"medium\": 500, \"bold\": 700)));\n}\n"
+);
+test!(
+    deep_merge_no_nesting,
+    r#"@use "sass:map";
+
+    a {
+        color: inspect(map.deep-merge($map1: (c: d), $map2: (1: 2)));
+    }"#,
+    "a {\n  color: (c: d, 1: 2);\n}\n"
+);
+test!(
+    deep_merge_positional,
+    r#"@use "sass:map";
+
+    a {
+        color: inspect(map.deep-merge((a: b), (c: d)));
+    }"#,
+    "a {\n  color: (a: b, c: d);\n}\n"
+);
+test!(
+    deep_merge_empty_maps,
+    r#"@use "sass:map";
+
+    a {
+        color: inspect(map.deep-merge((), ()));
+    }"#,
+    "a {\n  color: ();\n}\n"
+);
+test!(
+    deep_merge_empty_maps_bracketed_list,
+    r#"@use "sass:map";
+
+    a {
+        color: inspect(map.deep-merge([], []));
+    }"#,
+    "a {\n  color: ();\n}\n"
+);
+test!(
+    deep_merge_empty_first,
+    r#"@use "sass:map";
+
+    a {
+        color: inspect(map.deep-merge((a: b), ()));
+    }"#,
+    "a {\n  color: (a: b);\n}\n"
+);
+test!(
+    deep_merge_empty_second,
+    r#"@use "sass:map";
+
+    a {
+        color: inspect(map.deep-merge((), (a: b)));
+    }"#,
+    "a {\n  color: (a: b);\n}\n"
+);
+test!(
+    deep_merge_empty_deep,
+    r#"@use "sass:map";
+
+    a {
+        color: inspect(map.deep-merge((c: (d: e)), (c: ())));
+    }"#,
+    "a {\n  color: (c: (d: e));\n}\n"
+);
+test!(
+    deep_merge_empty_bracketed_list_deep,
+    r#"@use "sass:map";
+
+    a {
+        color: inspect(map.deep-merge((c: (d: e)), (c: [])));
+    }"#,
+    "a {\n  color: (c: (d: e));\n}\n"
+);
diff --git a/crates/lib/tests/map.rs b/crates/lib/tests/map.rs
index a991c96..967a1c2 100644
--- a/crates/lib/tests/map.rs
+++ b/crates/lib/tests/map.rs
@@ -120,66 +120,6 @@ test!(
     "a {b: inspect(map-merge((c: (d: (e: (f: (g: h))))), c, d, e, f, (g: 1)))}",
     "a {\n  b: (c: (d: (e: (f: (g: 1)))));\n}\n"
 );
-test!(
-    map_set_nested_empty,
-    "@use 'sass:map'; a {b: inspect(map.set((c: ()), c, d, e, f))}",
-    "a {\n  b: (c: (d: (e: f)));\n}\n"
-);
-test!(
-    map_set_update_existing,
-    "@use 'sass:map'; a {b: inspect(map.set((c: (d: e)), c, d, f))}",
-    "a {\n  b: (c: (d: f));\n}\n"
-);
-test!(
-    map_set_new_key,
-    "@use 'sass:map'; a {b: inspect(map.set((c: (d: e)), c, f, g))}",
-    "a {\n  b: (c: (d: e, f: g));\n}\n"
-);
-test!(
-    map_set_value_is_not_map,
-    "@use 'sass:map'; a {b: inspect(map.set((c: 1), c, d, f))}",
-    "a {\n  b: (c: (d: f));\n}\n"
-);
-test!(
-    map_merge_merge_into_map_with_many_keys,
-    r#"
-    @use "sass:map";
-
-    $fonts: (
-      "Helvetica": (
-        "weights": (
-          "regular": 400,
-          "medium": 500,
-          "bold": 700
-        )
-      )
-    );
-
-    a {
-        color: inspect(map.merge($fonts, "Helvetica", "weights", "regular", (a: 300)));
-    }"#,
-    "a {\n  color: (\"Helvetica\": (\"weights\": (\"regular\": (a: 300), \"medium\": 500, \"bold\": 700)));\n}\n"
-);
-test!(
-    map_merge_nested,
-    r#"
-    @use "sass:map";
-
-    $fonts: (
-      "Helvetica": (
-        "weights": (
-          "regular": 400,
-          "medium": 500,
-          "bold": 700
-        )
-      )
-    );
-
-    a {
-        color: inspect(map.set($fonts, "Helvetica", "weights", "regular", 300));
-    }"#,
-    "a {\n  color: (\"Helvetica\": (\"weights\": (\"regular\": 300, \"medium\": 500, \"bold\": 700)));\n}\n"
-);
 error!(
     map_merge_map1_non_map,
     "a {\n  color: map-merge(foo, (a: b));\n}\n", "Error: $map1: foo is not a map."
@@ -241,7 +181,6 @@ test!(
     "a {\n  color: 1, 2;\n}\n"
 );
 test!(
-    #[ignore = "blocked on rewriting inspect"]
     map_inspect_comma_separated_list_as_key,
     "a {\n  color: inspect(((1, 2): 3));\n}\n",
     "a {\n  color: ((1, 2): 3);\n}\n"