diff --git a/dlls/crypt32/serialize.c b/dlls/crypt32/serialize.c
index f55302d5129..32a9ca0006f 100644
--- a/dlls/crypt32/serialize.c
+++ b/dlls/crypt32/serialize.c
@@ -798,7 +798,7 @@ static BOOL CRYPT_SaveSerializedToMem(HCERTSTORE store,
  DWORD dwMsgAndCertEncodingType, void *handle)
 {
     CERT_BLOB *blob = (CERT_BLOB *)handle;
-    DWORD size;
+    DWORD size = 0;
     BOOL ret;
 
     ret = CRYPT_WriteSerializedStoreToStream(store, CRYPT_CountSerializedBytes,