diff --git a/src/builtin/functions/list.rs b/src/builtin/functions/list.rs
index 22aa996..4c55822 100644
--- a/src/builtin/functions/list.rs
+++ b/src/builtin/functions/list.rs
@@ -23,8 +23,8 @@ pub(crate) fn length(mut args: CallArgs, parser: &mut Parser<'_>) -> SassResult<
 pub(crate) fn nth(mut args: CallArgs, parser: &mut Parser<'_>) -> SassResult<Value> {
     args.max_args(2)?;
     let mut list = args.get_err(0, "list")?.as_list();
-    let n = match args.get_err(1, "n")? {
-        Value::Dimension(Some(num), ..) => num,
+    let (n, unit) = match args.get_err(1, "n")? {
+        Value::Dimension(Some(num), unit, ..) => (num, unit),
         Value::Dimension(None, u, ..) => {
             return Err((format!("$n: NaN{} is not an int.", u), args.span()).into())
         }
@@ -44,8 +44,9 @@ pub(crate) fn nth(mut args: CallArgs, parser: &mut Parser<'_>) -> SassResult<Val
     if n.abs() > Number::from(list.len()) {
         return Err((
             format!(
-                "$n: Invalid index {} for a list with {} elements.",
+                "$n: Invalid index {}{} for a list with {} elements.",
                 n,
+                unit,
                 list.len()
             ),
             args.span(),
@@ -83,8 +84,8 @@ pub(crate) fn set_nth(mut args: CallArgs, parser: &mut Parser<'_>) -> SassResult
         Value::Map(m) => (m.as_list(), ListSeparator::Comma, Brackets::None),
         v => (vec![v], ListSeparator::Space, Brackets::None),
     };
-    let n = match args.get_err(1, "n")? {
-        Value::Dimension(Some(num), ..) => num,
+    let (n, unit) = match args.get_err(1, "n")? {
+        Value::Dimension(Some(num), unit, ..) => (num, unit),
         Value::Dimension(None, u, ..) => {
             return Err((format!("$n: NaN{} is not an int.", u), args.span()).into())
         }
@@ -105,7 +106,10 @@ pub(crate) fn set_nth(mut args: CallArgs, parser: &mut Parser<'_>) -> SassResult
 
     if n.abs() > Number::from(len) {
         return Err((
-            format!("$n: Invalid index {} for a list with {} elements.", n, len),
+            format!(
+                "$n: Invalid index {}{} for a list with {} elements.",
+                n, unit, len
+            ),
             args.span(),
         )
             .into());
diff --git a/src/builtin/functions/math.rs b/src/builtin/functions/math.rs
index 84a51ee..2c19c08 100644
--- a/src/builtin/functions/math.rs
+++ b/src/builtin/functions/math.rs
@@ -17,7 +17,7 @@ pub(crate) fn percentage(mut args: CallArgs, parser: &mut Parser<'_>) -> SassRes
     args.max_args(1)?;
     let num = match args.get_err(0, "number")? {
         Value::Dimension(Some(n), Unit::None, _) => Some(n * Number::from(100)),
-        Value::Dimension(None, ..) => None,
+        Value::Dimension(None, Unit::None, _) => None,
         v @ Value::Dimension(..) => {
             return Err((
                 format!(
diff --git a/src/builtin/functions/string.rs b/src/builtin/functions/string.rs
index eb58b4e..4fc40ba 100644
--- a/src/builtin/functions/string.rs
+++ b/src/builtin/functions/string.rs
@@ -110,8 +110,8 @@ pub(crate) fn str_slice(mut args: CallArgs, parser: &mut Parser<'_>) -> SassResu
         Value::Dimension(Some(n), Unit::None, _) => (n.to_integer() + BigInt::from(str_len + 1))
             .to_usize()
             .unwrap(),
-        Value::Dimension(None, u, ..) => {
-            return Err((format!("NaN{} is not an int.", u), args.span()).into())
+        Value::Dimension(None, Unit::None, ..) => {
+            return Err(("NaN is not an int.", args.span()).into())
         }
         v @ Value::Dimension(..) => {
             return Err((
@@ -143,8 +143,8 @@ pub(crate) fn str_slice(mut args: CallArgs, parser: &mut Parser<'_>) -> SassResu
         Value::Dimension(Some(n), Unit::None, _) => (n.to_integer() + BigInt::from(str_len + 1))
             .to_usize()
             .unwrap_or(str_len + 1),
-        Value::Dimension(None, u, ..) => {
-            return Err((format!("NaN{} is not an int.", u), args.span()).into())
+        Value::Dimension(None, Unit::None, ..) => {
+            return Err(("NaN is not an int.", args.span()).into())
         }
         v @ Value::Dimension(..) => {
             return Err((
@@ -243,8 +243,8 @@ pub(crate) fn str_insert(mut args: CallArgs, parser: &mut Parser<'_>) -> SassRes
             return Err((format!("$index: {} is not an int.", n), args.span()).into())
         }
         Value::Dimension(Some(n), Unit::None, _) => n,
-        Value::Dimension(None, u, ..) => {
-            return Err((format!("$index: NaN{} is not an int.", u), args.span()).into())
+        Value::Dimension(None, Unit::None, ..) => {
+            return Err(("$index: NaN is not an int.", args.span()).into())
         }
         v @ Value::Dimension(..) => {
             return Err((
diff --git a/tests/list.rs b/tests/list.rs
index 9f5a678..8475db5 100644
--- a/tests/list.rs
+++ b/tests/list.rs
@@ -338,3 +338,12 @@ error!(
     invalid_item_in_comma_separated_list_inside_interpolation,
     "a {\n  color: #{red, color * #abc};\n}\n", "Error: Undefined operation \"color * #abc\"."
 );
+error!(
+    nth_invalid_index_message_contains_unit,
+    "a {\n  color: nth([], 1px);\n}\n", "Error: $n: Invalid index 1px for a list with 0 elements."
+);
+error!(
+    set_nth_invalid_index_message_contains_unit,
+    "a {\n  color: set-nth([], 1px, a);\n}\n",
+    "Error: $n: Invalid index 1px for a list with 0 elements."
+);
diff --git a/tests/nan.rs b/tests/nan.rs
index 9b5ef7d..a937a26 100644
--- a/tests/nan.rs
+++ b/tests/nan.rs
@@ -77,3 +77,85 @@ test!(
     "$n: (0/0);\na {\n  color: max(1px, $n, 0);\n}\n",
     "a {\n  color: 1px;\n}\n"
 );
+error!(
+    unitful_nan_str_slice_start,
+    "@use \"sass:math\";\na {\n  color: str-slice(\"\", math.acos(2));\n}\n",
+    "Error: $start: Expected NaNdeg to have no units."
+);
+error!(
+    unitful_nan_str_slice_end,
+    "@use \"sass:math\";\na {\n  color: str-slice(\"\", 0, math.acos(2));\n}\n",
+    "Error: $end: Expected NaNdeg to have no units."
+);
+error!(
+    unitful_nan_str_insert_index,
+    "@use \"sass:math\";\na {\n  color: str-insert(\"\", \"\", math.acos(2));\n}\n",
+    "Error: $index: Expected NaNdeg to have no units."
+);
+error!(
+    unitful_nan_percentage,
+    "@use \"sass:math\";\na {\n  color: percentage(math.acos(2));\n}\n",
+    "Error: $number: Expected NaNdeg to have no units."
+);
+error!(
+    unitful_nan_round,
+    "@use \"sass:math\";\na {\n  color: round(math.acos(2));\n}\n", "Error: Infinity or NaN toInt"
+);
+error!(
+    unitful_nan_ceil,
+    "@use \"sass:math\";\na {\n  color: ceil(math.acos(2));\n}\n", "Error: Infinity or NaN toInt"
+);
+error!(
+    unitful_nan_floor,
+    "@use \"sass:math\";\na {\n  color: floor(math.acos(2));\n}\n", "Error: Infinity or NaN toInt"
+);
+test!(
+    unitful_nan_abs,
+    "@use \"sass:math\";\na {\n  color: abs(math.acos(2));\n}\n",
+    "a {\n  color: NaNdeg;\n}\n"
+);
+error!(
+    unitful_nan_random,
+    "@use \"sass:math\";\na {\n  color: random(math.acos(2));\n}\n",
+    "Error: $limit: NaNdeg is not an int."
+);
+test!(
+    unitful_nan_min_first_arg,
+    "@use \"sass:math\";\na {\n  color: min(math.acos(2), 1px);\n}\n",
+    "a {\n  color: NaNdeg;\n}\n"
+);
+test!(
+    unitful_nan_min_last_arg,
+    "@use \"sass:math\";\na {\n  color: min(1px, math.acos(2));\n}\n",
+    "a {\n  color: 1px;\n}\n"
+);
+test!(
+    unitful_nan_min_middle_arg,
+    "@use \"sass:math\";\na {\n  color: min(1px, math.acos(2), 0);\n}\n",
+    "a {\n  color: 0;\n}\n"
+);
+test!(
+    unitful_nan_max_first_arg,
+    "@use \"sass:math\";\na {\n  color: max(math.acos(2), 1px);\n}\n",
+    "a {\n  color: NaNdeg;\n}\n"
+);
+test!(
+    unitful_nan_max_last_arg,
+    "@use \"sass:math\";\na {\n  color: max(1px, math.acos(2));\n}\n",
+    "a {\n  color: 1px;\n}\n"
+);
+test!(
+    unitful_nan_max_middle_arg,
+    "@use \"sass:math\";\na {\n  color: max(1px, math.acos(2), 0);\n}\n",
+    "a {\n  color: 1px;\n}\n"
+);
+error!(
+    unitful_nan_nth_n,
+    "@use \"sass:math\";\na {\n  color: nth([a], math.acos(2));\n}\n",
+    "Error: $n: NaNdeg is not an int."
+);
+error!(
+    unitful_nan_set_nth_n,
+    "@use \"sass:math\";\na {\n  color: set-nth([a], math.acos(2), b);\n}\n",
+    "Error: $n: NaNdeg is not an int."
+);