diff --git a/openmc/data/endf.py b/openmc/data/endf.py
index 0c590be0a8..c0049f9773 100644
--- a/openmc/data/endf.py
+++ b/openmc/data/endf.py
@@ -27,7 +27,7 @@ LIBRARIES = {0: 'ENDF/B', 1: 'ENDF/A', 2: 'JEFF', 3: 'EFF',
              35: 'BROND', 36: 'INGDB-90', 37: 'FENDL/A', 41: 'BROND'}
 
 SUM_RULES = {1: [2, 3],
-             3: [4, 5, 11, 16, 17, 22, 23, 24, 25, 28, 29, 30, 32, 33, 34, 35,
+             3: [4, 5, 11, 16, 17, 22, 23, 24, 25, 27, 28, 29, 30, 32, 33, 34, 35,
                  36, 37, 41, 42, 44, 45, 152, 153, 154, 156, 157, 158, 159, 160,
                  161, 162, 163, 164, 165, 166, 167, 168, 169, 170, 171, 172,
                  173, 174, 175, 176, 177, 178, 179, 180, 181, 183, 184, 185,
@@ -35,7 +35,7 @@ SUM_RULES = {1: [2, 3],
              4: list(range(50, 92)),
              16: list(range(875, 892)),
              18: [19, 20, 21, 38],
-             27: [8, 101],
+             27: [18, 101],
              101: [102, 103, 104, 105, 106, 107, 108, 109, 111, 112, 113, 114,
                    115, 116, 117, 155, 182, 191, 192, 193, 197],
              103: list(range(600, 650)),