diff --git a/lib/compress/zstd_compress.c b/lib/compress/zstd_compress.c
index 2511ab29e..892912f2e 100644
--- a/lib/compress/zstd_compress.c
+++ b/lib/compress/zstd_compress.c
@@ -38,9 +38,7 @@
 *  Helper functions
 ***************************************/
 size_t ZSTD_compressBound(size_t srcSize) {
-    size_t const lowLimit = 256 KB;
-    size_t const margin = (srcSize < lowLimit) ? (lowLimit-srcSize) >> 12 : 0;  /* from 64 to 0 */
-    return srcSize + (srcSize >> 8) + margin;
+    return ZSTD_COMPRESSBOUND(srcSize);
 }
 
 
diff --git a/lib/zstd.h b/lib/zstd.h
index 02241fd3f..4e225bb5e 100644
--- a/lib/zstd.h
+++ b/lib/zstd.h
@@ -131,10 +131,11 @@ ZSTDLIB_API unsigned long long ZSTD_getDecompressedSize(const void* src, size_t
 
 
 /*======  Helper functions  ======*/
-ZSTDLIB_API int         ZSTD_maxCLevel(void);               /*!< maximum compression level available */
+#define ZSTD_COMPRESSBOUND(srcSize)   ((srcSize) + ((srcSize)>>8) + (((srcSize) < 128 KB) ? ((128 KB - (srcSize)) >> 11) /* margin, from 64 to 0 */ : 0))  /* this formula ensures that bound(A) + bound(B) <= bound(A+B) as long as A and B >= 128 KB */
 ZSTDLIB_API size_t      ZSTD_compressBound(size_t srcSize); /*!< maximum compressed size in worst case scenario */
 ZSTDLIB_API unsigned    ZSTD_isError(size_t code);          /*!< tells if a `size_t` function result is an error code */
 ZSTDLIB_API const char* ZSTD_getErrorName(size_t code);     /*!< provides readable string from an error code */
+ZSTDLIB_API int         ZSTD_maxCLevel(void);               /*!< maximum compression level available */
 
 
 /***************************************