diff --git a/pygeofilter/parsers/ecql/grammar.lark b/pygeofilter/parsers/ecql/grammar.lark
index 75611d9..bb1314a 100644
--- a/pygeofilter/parsers/ecql/grammar.lark
+++ b/pygeofilter/parsers/ecql/grammar.lark
@@ -109,7 +109,7 @@ period: DATETIME "/" DATETIME
 
 envelope: "ENVELOPE" "(" number number number number ")"
 
-BOOLEAN: ( "TRUE" | "FALSE" )
+BOOLEAN.2: ( "TRUE"i | "FALSE"i )
 
 DOUBLE_QUOTED: "\"" /.*?/ "\""
 SINGLE_QUOTED: "'" /.*?/ "'"
diff --git a/pygeofilter/parsers/ecql/parser.py b/pygeofilter/parsers/ecql/parser.py
index 48a2b63..c1a8731 100644
--- a/pygeofilter/parsers/ecql/parser.py
+++ b/pygeofilter/parsers/ecql/parser.py
@@ -181,7 +181,7 @@ def FLOAT(self, value):
         return float(value)
 
     def BOOLEAN(self, value):
-        return value == "TRUE"
+        return value.lower() == "true"
 
     def DOUBLE_QUOTED(self, token):
         return token[1:-1]
diff --git a/tests/parsers/ecql/test_parser.py b/tests/parsers/ecql/test_parser.py
index 9d12010..5266b23 100644
--- a/tests/parsers/ecql/test_parser.py
+++ b/tests/parsers/ecql/test_parser.py
@@ -597,3 +597,35 @@ def test_function_attr_string_arg():
             ],
         ),
     )
+
+
+def test_attribute_eq_true_uppercase():
+    result = parse("attr = TRUE")
+    assert result == ast.Equal(
+        ast.Attribute("attr"),
+        True,
+    )
+
+
+def test_attribute_eq_true_lowercase():
+    result = parse("attr = true")
+    assert result == ast.Equal(
+        ast.Attribute("attr"),
+        True,
+    )
+
+
+def test_attribute_eq_false_uppercase():
+    result = parse("attr = FALSE")
+    assert result == ast.Equal(
+        ast.Attribute("attr"),
+        False,
+    )
+
+
+def test_attribute_eq_false_lowercase():
+    result = parse("attr = false")
+    assert result == ast.Equal(
+        ast.Attribute("attr"),
+        False,
+    )