diff --git a/src/util/virstoragefile.c b/src/util/virstoragefile.c
index 1b4d4cf85e2ce69f27c3798765db4136c2d16c8b..8f04b7839295a69d60091ca4b96cf890050b359a 100644
--- a/src/util/virstoragefile.c
+++ b/src/util/virstoragefile.c
@@ -671,8 +671,13 @@ virStorageFileMatchesVersion(int format,
 static bool
 virBackingStoreIsFile(const char *backing)
 {
-    /* Backing store is a network block device or Rados block device */
-    if (STRPREFIX(backing, "nbd:") || STRPREFIX(backing, "rbd:"))
+    char *colon = strchr(backing, ':');
+    char *slash = strchr(backing, '/');
+
+    /* Reject anything that looks like a protocol (such as nbd: or
+     * rbd:); if someone really does want a relative file name that
+     * includes ':', they can always prefix './'.  */
+    if (colon && (!slash || colon < slash))
         return false;
     return true;
 }