diff --git a/common.rc b/common.rc
index 3d2cd32f..47ee1e33 100644
--- a/common.rc
+++ b/common.rc
@@ -630,7 +630,10 @@ _check_filesystem()
 
 _check_test_fs()
 {
-    _check_filesystem $TEST_DEV $TEST_LOGDEV
+    TEST_LOG=""
+    [ "$USE_EXTERNAL" = yes -a ! -z "$TEST_LOGDEV" ] && \
+        TEST_LOG="$TEST_LOGDEV"
+    _check_filesystem $TEST_DEV $TEST_LOG
 }
 
 _check_scratch_fs()