diff --git a/formats/aci.py b/formats/aci.py
index 05f1dce3e..ea108830f 100644
--- a/formats/aci.py
+++ b/formats/aci.py
@@ -3,6 +3,7 @@ from util.streamlayerformat import StreamLayerMerger
 from formats.tarimageformatter import TarImageFormatter
 
 import json
+import re
 
 class ACIImage(TarImageFormatter):
   """ Image formatter which produces an ACI-compatible TAR.
@@ -46,10 +47,11 @@ class ACIImage(TarImageFormatter):
         "value": str(cpu)
       }
 
-    def _isolate_capabilities(capabilities_set):
+    def _isolate_capabilities(capabilities_set_value):
+      capabilities_set = re.split(r'[\s,]', capabilities_set_value)
       return {
         "name": "capabilities/bounding-set",
-        "value": str(capabilities_set)
+        "value": ' '.join(capabilities_set)
       }
 
     mappers = {