diff --git a/confluent_server/confluent/osimage.py b/confluent_server/confluent/osimage.py
index 33062708..fda01d82 100644
--- a/confluent_server/confluent/osimage.py
+++ b/confluent_server/confluent/osimage.py
@@ -834,7 +834,7 @@ def fingerprint_initramfs(archive):
     return None
 
 
-async def scan_iso(archive):
+def scan_iso(archive):
     scanudf = False
     filesizes = {}
     filecontents = {}
@@ -845,7 +845,6 @@ async def scan_iso(archive):
             for ent in reader:
                 if str(ent).endswith('TRANS.TBL'):
                     continue
-                await asyncio.sleep(0)
                 filesizes[str(ent)] = ent.size
                 if str(ent) == 'README.TXT':
                     readmecontents = b''
@@ -909,13 +908,13 @@ def parse_bfb(archive):
             archive.seek(currsize, os.SEEK_CUR)
     return None
 
-async def fingerprint(archive):
+def fingerprint(archive):
     archive.seek(0)
     header = archive.read(32768)
     archive.seek(32769)
     if archive.read(6) == b'CD001\x01':
         # ISO image
-        isoinfo = await scan_iso(archive)
+        isoinfo = scan_iso(archive)
         name = None
         for fun in globals():
             if fun.startswith('check_'):
@@ -947,7 +946,7 @@ async def import_image(filename, callback, backend=False, mfd=None, custtargpath
         archive = os.fdopen(int(mfd), 'rb')
     else:
         archive = open(filename, 'rb')
-    identity = await fingerprint(archive)
+    identity = await asyncio.to_thread(fingerprint, archive)
     if not identity:
         return -1
     identity, imginfo, funname = identity
@@ -1207,7 +1206,7 @@ class MediaImporter(object):
         else:
             medfile = open(media, 'rb')
         try:
-            identity = await fingerprint(medfile)
+            identity = await asyncio.to_thread(fingerprint, medfile)
         finally:
             if not self.medfile:
                 medfile.close()