diff --git a/src/value/ops.rs b/src/value/ops.rs
index 5273d70..d030f3c 100644
--- a/src/value/ops.rs
+++ b/src/value/ops.rs
@@ -60,6 +60,10 @@ impl Value {
                     format!("{}{}{}", num, unit, other.to_css_string(span)?),
                     QuoteKind::None,
                 ),
+                Self::True | Self::False => Self::Ident(
+                    format!("{}{}{}", num, unit, other.to_css_string(span)?),
+                    QuoteKind::None,
+                ),
                 _ => {
                     return Err((
                         format!(
diff --git a/tests/addition.rs b/tests/addition.rs
index 22dcbfc..ab5a45b 100644
--- a/tests/addition.rs
+++ b/tests/addition.rs
@@ -253,3 +253,13 @@ test!(
     "a {\n  color: foo + #fff;\n}\n",
     "a {\n  color: foo#fff;\n}\n"
 );
+test!(
+    num_plus_true,
+    "a {\n  color: 1 + true;\n}\n",
+    "a {\n  color: 1true;\n}\n"
+);
+test!(
+    num_plus_false,
+    "a {\n  color: 1 + false;\n}\n",
+    "a {\n  color: 1false;\n}\n"
+);