diff --git a/tests/qemu-iotests/iotests.py b/tests/qemu-iotests/iotests.py
index 9351f9c6ac..56aa068277 100644
--- a/tests/qemu-iotests/iotests.py
+++ b/tests/qemu-iotests/iotests.py
@@ -277,6 +277,38 @@ def ordered_qmp(qmsg, conv_keys=True):
 def qemu_img_create(*args: str) -> 'subprocess.CompletedProcess[str]':
     return qemu_img('create', *args)
 
+def qemu_img_json(*args: str) -> Any:
+    """
+    Run qemu-img and return its output as deserialized JSON.
+
+    :raise CalledProcessError:
+        When qemu-img crashes, or returns a non-zero exit code without
+        producing a valid JSON document to stdout.
+    :raise JSONDecoderError:
+        When qemu-img returns 0, but failed to produce a valid JSON document.
+
+    :return: A deserialized JSON object; probably a dict[str, Any].
+    """
+    try:
+        res = qemu_img(*args, combine_stdio=False)
+    except subprocess.CalledProcessError as exc:
+        # Terminated due to signal. Don't bother.
+        if exc.returncode < 0:
+            raise
+
+        # Commands like 'check' can return failure (exit codes 2 and 3)
+        # to indicate command completion, but with errors found. For
+        # multi-command flexibility, ignore the exact error codes and
+        # *try* to load JSON.
+        try:
+            return json.loads(exc.stdout)
+        except json.JSONDecodeError:
+            # Nope. This thing is toast. Raise the /process/ error.
+            pass
+        raise
+
+    return json.loads(res.stdout)
+
 def qemu_img_measure(*args):
     return json.loads(qemu_img_pipe("measure", "--output", "json", *args))