diff --git a/src/p_vmlinz.cpp b/src/p_vmlinz.cpp
index c0cf7122..181c73df 100644
--- a/src/p_vmlinz.cpp
+++ b/src/p_vmlinz.cpp
@@ -123,6 +123,9 @@ int PackVmlinuzI386::uncompressKernel()
     fi->seek(0, SEEK_SET);
     fi->readx(obuf, file_size);
 
+    if (find_le32(obuf + setup_size, UPX_MIN(file_size - setup_size, 1024), UPX_MAGIC_LE32) >= 0)
+        throwAlreadyPacked();
+
     // estimate gzip-uncompressed kernel size & alloc buffer
     ibuf.alloc((file_size - setup_size) * 3);