diff --git a/tests/qemu-iotests/iotests.py b/tests/qemu-iotests/iotests.py
index 936d33df61..a4a2238b42 100644
--- a/tests/qemu-iotests/iotests.py
+++ b/tests/qemu-iotests/iotests.py
@@ -921,9 +921,17 @@ def qemu_pipe(*args):
 def supported_formats(read_only=False):
     '''Set 'read_only' to True to check ro-whitelist
        Otherwise, rw-whitelist is checked'''
-    format_message = qemu_pipe("-drive", "format=help")
-    line = 1 if read_only else 0
-    return format_message.splitlines()[line].split(":")[1].split()
+
+    if not hasattr(supported_formats, "formats"):
+        supported_formats.formats = {}
+
+    if read_only not in supported_formats.formats:
+        format_message = qemu_pipe("-drive", "format=help")
+        line = 1 if read_only else 0
+        supported_formats.formats[read_only] = \
+            format_message.splitlines()[line].split(":")[1].split()
+
+    return supported_formats.formats[read_only]
 
 def skip_if_unsupported(required_formats=[], read_only=False):
     '''Skip Test Decorator