diff --git a/cli/src/pcluster/constants.py b/cli/src/pcluster/constants.py
index 33485649e8..019da2428d 100644
--- a/cli/src/pcluster/constants.py
+++ b/cli/src/pcluster/constants.py
@@ -364,7 +364,9 @@ class Operation(Enum):
 CAPACITY_BLOCK_INACTIVE_STATES = ["scheduled", "payment-pending", "assessing", "delayed"]
 
 # Older generation instance types
+# This constant is only used by test code
 EXCLUDED_INSTANCE_TYPE_PREFIXES = (
+    "a1",  # a1 is based on Graviton 1 which is not supported by the newer version of Amazon Linux 2023
     "m1",
     "m2",
     "m3",