diff --git a/rdflib/term.py b/rdflib/term.py
index 5dd69b9e9..b6bc26460 100644
--- a/rdflib/term.py
+++ b/rdflib/term.py
@@ -1481,7 +1481,7 @@ def _castPythonToLiteral(obj):
     URIRef(_XSD_PFX + 'normalizedString'): None,
     URIRef(_XSD_PFX + 'token'): None,
     URIRef(_XSD_PFX + 'language'): None,
-    URIRef(_XSD_PFX + 'boolean'): lambda i: i.lower() in ['1', 'true'],
+    URIRef(_XSD_PFX + 'boolean'): lambda i: i.lower() == 'true',
     URIRef(_XSD_PFX + 'decimal'): Decimal,
     URIRef(_XSD_PFX + 'integer'): long_type,
     URIRef(_XSD_PFX + 'nonPositiveInteger'): int,