diff --git a/.changes/next-release/bugfix-emr-20663.json b/.changes/next-release/bugfix-emr-20663.json
new file mode 100644
index 000000000000..010dd74fb6e8
--- /dev/null
+++ b/.changes/next-release/bugfix-emr-20663.json
@@ -0,0 +1,5 @@
+{
+  "type": "bugfix",
+  "category": "emr",
+  "description": "Fixed the ARN partition suffix returned by ``get_policy_arn_suffix`` for AWS ISO (``aws-iso``, ``aws-iso-b``, ``aws-iso-e``, ``aws-iso-f``) and European Sovereign Cloud (``aws-eusc``) regions, so ``emr create-default-roles``, ``dlm create-default-role`` and ``emr-containers update-role-trust-policy`` build valid IAM policy ARNs in those partitions instead of defaulting to ``aws``."
+}
diff --git a/awscli/customizations/utils.py b/awscli/customizations/utils.py
index c5055418c4c3..4f81b3c9bfef 100644
--- a/awscli/customizations/utils.py
+++ b/awscli/customizations/utils.py
@@ -226,5 +226,17 @@ def get_policy_arn_suffix(region):
         return "aws-cn"
     elif region_string.startswith("us-gov"):
         return "aws-us-gov"
+    # The isob/isof prefixes must be checked before the more general "us-iso"
+    # prefix, since "us-isob-east-1" also starts with "us-iso".
+    elif region_string.startswith("us-isob"):
+        return "aws-iso-b"
+    elif region_string.startswith("us-isof"):
+        return "aws-iso-f"
+    elif region_string.startswith("us-iso"):
+        return "aws-iso"
+    elif region_string.startswith("eu-isoe"):
+        return "aws-iso-e"
+    elif region_string.startswith("eusc-"):
+        return "aws-eusc"
     else:
         return "aws"
diff --git a/tests/unit/customizations/test_utils.py b/tests/unit/customizations/test_utils.py
index 8b003361e090..7d7513e9c3a6 100644
--- a/tests/unit/customizations/test_utils.py
+++ b/tests/unit/customizations/test_utils.py
@@ -267,3 +267,18 @@ def test_get_policy_arn_suffix(self):
         self.assertEqual("aws", utils.get_policy_arn_suffix("us-east-1"))
         self.assertEqual("aws", utils.get_policy_arn_suffix("sa-east-1"))
         self.assertEqual("aws", utils.get_policy_arn_suffix("ap-south-1"))
+        self.assertEqual(
+            "aws-iso", utils.get_policy_arn_suffix("us-iso-east-1")
+        )
+        self.assertEqual(
+            "aws-iso-b", utils.get_policy_arn_suffix("us-isob-east-1")
+        )
+        self.assertEqual(
+            "aws-iso-e", utils.get_policy_arn_suffix("eu-isoe-west-1")
+        )
+        self.assertEqual(
+            "aws-iso-f", utils.get_policy_arn_suffix("us-isof-south-1")
+        )
+        self.assertEqual(
+            "aws-eusc", utils.get_policy_arn_suffix("eusc-de-east-1")
+        )