diff --git a/src/storage/storage_backend.c b/src/storage/storage_backend.c
index bb58d4a6177c90ed857a7b94b93d6107c8a3f6a9..2551f1f56f89d2cde3b0a2bda6f5428ef2cd94dd 100644
--- a/src/storage/storage_backend.c
+++ b/src/storage/storage_backend.c
@@ -652,7 +652,12 @@ virStorageBackendCreateQemuImgCmd(virConnectPtr conn,
     unsigned long long int size_arg;
     bool preallocate = false;
 
-    const char *type = virStorageFileFormatTypeToString(vol->target.format);
+    /* Treat output block devices as 'raw' format */
+    const char *type =
+        virStorageFileFormatTypeToString(vol->type == VIR_STORAGE_VOL_BLOCK ?
+                                         VIR_STORAGE_FILE_RAW :
+                                         vol->target.format);
+
     const char *backingType = vol->backingStore.path ?
         virStorageFileFormatTypeToString(vol->backingStore.format) : NULL;