diff -uNrp libvirt-0.9.7.orig/src/qemu/qemu_driver.c libvirt-0.9.7/src/qemu/qemu_driver.c
--- libvirt-0.9.7.orig/src/qemu/qemu_driver.c	2011-10-31 12:46:04.000000000 +0900
+++ libvirt-0.9.7/src/qemu/qemu_driver.c	2011-11-07 13:03:07.162639142 +0900
@@ -8976,6 +8976,25 @@ cleanup:
     return ret;
 }
 
+static int ATTRIBUTE_NONNULL(1)
+qemuDomainSnapshotCheckSrcQcow2(const char *src)
+{
+    const char *qemuimgarg[] = {NULL, "check", "-f", "qcow2", NULL, NULL};
+    int ret = -1;
+
+    qemuimgarg[0] = virFindFileInPath("qemu-img");
+    if (!qemuimgarg[0]) {
+        qemuReportError(VIR_ERR_INTERNAL_ERROR,
+                        "%s", _("unable to find qemu-img"));
+        return ret;
+    }
+    qemuimgarg[4] = src;
+
+    ret = virRun(qemuimgarg, NULL);
+    VIR_FREE(qemuimgarg[0]);
+    return ret;
+}
+
 /* The domain is expected to hold monitor lock.  */
 static int
 qemuDomainSnapshotCreateSingleDiskActive(struct qemud_driver *driver,
@@ -9002,6 +9021,13 @@ qemuDomainSnapshotCreateSingleDiskActive
         return -1;
     }
 
+    ret = qemuDomainSnapshotCheckSrcQcow2(src->disk);
+    if (ret) {
+        qemuReportError(VIR_ERR_INTERNAL_ERROR,
+                        "%s", _("src image is not qcow2 format"));
+        return ret;
+    }
+
     if (virAsprintf(&device, "drive-%s", disk->info.alias) < 0 ||
         !(source = strdup(snap->file)) ||
         (STRNEQ_NULLABLE(disk->driverType, "qcow2") &&