diff --git a/lib/compress/zstd_compress.c b/lib/compress/zstd_compress.c
index 8993e7d7..937fd310 100644
--- a/lib/compress/zstd_compress.c
+++ b/lib/compress/zstd_compress.c
@@ -153,7 +153,7 @@ ZSTD_CCtx* ZSTD_createCCtx_advanced(ZSTD_customMem customMem)
     cctx->customMem = customMem;
     cctx->compressionLevel = ZSTD_CLEVEL_DEFAULT;
     ZSTD_STATIC_ASSERT(zcss_init==0);
-    ZSTD_STATIC_ASSERT(ZSTD_CONTENTSIZE_UNKNOWN==(U64)(-(1ULL)));
+    ZSTD_STATIC_ASSERT(ZSTD_CONTENTSIZE_UNKNOWN==(0ULL - 1));
     return cctx;
 }