diff --git a/include/minja/minja.hpp b/include/minja/minja.hpp
index ec89bc7..39821cd 100644
--- a/include/minja/minja.hpp
+++ b/include/minja/minja.hpp
@@ -1306,6 +1306,8 @@ class BinaryOpExpr : public Expression {
               if (name == "iterable") return l.is_iterable();
               if (name == "sequence") return l.is_array();
               if (name == "defined") return !l.is_null();
+              if (name == "true") return l.to_bool();
+              if (name == "false") return !l.to_bool();
               throw std::runtime_error("Unknown type for 'is' operator: " + name);
             };
             auto value = eval();
diff --git a/tests/test-syntax.cpp b/tests/test-syntax.cpp
index 5bc82fa..a5a2707 100644
--- a/tests/test-syntax.cpp
+++ b/tests/test-syntax.cpp
@@ -217,6 +217,18 @@ TEST(SyntaxTest, SimpleCases) {
     EXPECT_EQ(
         "False",
         render(R"({% set foo = true %}{{ not foo is defined }})", {}, {}));
+    EXPECT_EQ(
+        "True",
+        render(R"({% set foo = true %}{{ foo is true }})", {}, {}));
+    EXPECT_EQ(
+        "False",
+        render(R"({% set foo = true %}{{ foo is false }})", {}, {}));
+    EXPECT_EQ(
+        "True",
+        render(R"({% set foo = false %}{{ foo is not true }})", {}, {}));
+    EXPECT_EQ(
+        "False",
+        render(R"({% set foo = false %}{{ foo is not false }})", {}, {}));
     EXPECT_EQ(
         R"({"a": "b"})",
         render(R"({{ {"a": "b"} | tojson }})", {}, {}));