diff --git a/rdflib/xsd_datetime.py b/rdflib/xsd_datetime.py
index 44af2172d..a5d08c3b4 100644
--- a/rdflib/xsd_datetime.py
+++ b/rdflib/xsd_datetime.py
@@ -129,7 +129,7 @@ def __init__(
             years = Decimal(str(years))
         new_years, months = fquotmod(months, 0, 12)
         self.months = months
-        self.years = Decimal(new_years)
+        self.years = Decimal(years+new_years)
         self.tdelta = timedelta(
             days, seconds, microseconds, milliseconds, minutes, hours, weeks
         )
diff --git a/test/test_sparql/test_datetime_processing.py b/test/test_sparql/test_datetime_processing.py
index c934e9543..7fd0b2a6c 100644
--- a/test/test_sparql/test_datetime_processing.py
+++ b/test/test_sparql/test_datetime_processing.py
@@ -94,8 +94,8 @@ def test_datetime_duration_subs():
     SELECT (?d - ?duration AS ?next_year)
     WHERE {
         VALUES (?duration ?d) {
-            ("P1Y"^^xsd:yearMonthDuration"2019-05-28T12:14:45Z"^^xsd:dateTime)
-            ("P1Y"^^xsd:yearMonthDuration"2019-05-28"^^xsd:date)
+            ("P1Y"^^xsd:yearMonthDuration "2019-05-28T12:14:45Z"^^xsd:dateTime)
+            ("P1Y"^^xsd:yearMonthDuration "2019-05-28"^^xsd:date)
         }
     }
     """