diff --git a/lib/decompress/zstd_decompress.c b/lib/decompress/zstd_decompress.c
index 4c47930c..b6a3865c 100644
--- a/lib/decompress/zstd_decompress.c
+++ b/lib/decompress/zstd_decompress.c
@@ -193,7 +193,24 @@ static void ZSTD_refDCtx(ZSTD_DCtx* dstDCtx, const ZSTD_DCtx* srcDCtx)
 *   Decompression section
 ***************************************************************/
 
-/* See compression format details in : doc/zstd_compression_format.md */
+/*! ZSTD_isFrame() :
+ *  Tells if the content of `buffer` starts with a valid Frame Identifier.
+ *  Note : Frame Identifier is 4 bytes. If `size < 4`, @return will always be 0.
+ *  Note 2 : Legacy Frame Identifiers are considered valid only if Legacy Support is enabled.
+ *  Note 3 : Skippable Frame Identifiers are considered valid. */
+unsigned ZSTD_isFrame(const void* buffer, size_t size)
+{
+    if (size < 4) return 0;
+    {   U32 const magic = MEM_readLE32(buffer);
+        if (magic == ZSTD_MAGICNUMBER) return 1;
+        if ((magic & 0xFFFFFFF0U) == ZSTD_MAGIC_SKIPPABLE_START) return 1;
+    }
+#if defined(ZSTD_LEGACY_SUPPORT) && (ZSTD_LEGACY_SUPPORT >= 1)
+    if (ZSTD_isLegacy(buffer, size)) return 1;
+#endif
+    return 0;
+}
+
 
 /** ZSTD_frameHeaderSize() :
 *   srcSize must be >= ZSTD_frameHeaderSize_prefix.
diff --git a/lib/zstd.h b/lib/zstd.h
index ea5caf14..c18fd0d3 100644
--- a/lib/zstd.h
+++ b/lib/zstd.h
@@ -433,6 +433,13 @@ ZSTDLIB_API size_t ZSTD_compress_advanced (ZSTD_CCtx* ctx,
 
 /*--- Advanced decompression functions ---*/
 
+/*! ZSTD_isFrame() :
+ *  Tells if the content of `buffer` starts with a valid Frame Identifier.
+ *  Note : Frame Identifier is 4 bytes. If `size < 4`, @return will always be 0.
+ *  Note 2 : Legacy Frame Identifiers are considered valid only if Legacy Support is enabled.
+ *  Note 3 : Skippable Frame Identifiers are considered valid. */
+ZSTDLIB_API unsigned ZSTD_isFrame(const void* buffer, size_t size);
+
 /*! ZSTD_estimateDCtxSize() :
  *  Gives the potential amount of memory allocated to create a ZSTD_DCtx */
 ZSTDLIB_API size_t ZSTD_estimateDCtxSize(void);
diff --git a/programs/fileio.c b/programs/fileio.c
index c4c308e0..fe321015 100644
--- a/programs/fileio.c
+++ b/programs/fileio.c
@@ -8,16 +8,6 @@
  */
 
 
-/* *************************************
- *  Tuning options
- ***************************************/
-#ifndef ZSTD_LEGACY_SUPPORT
-/* LEGACY_SUPPORT :
- *  decompressor can decode older formats (starting from zstd 0.1+) */
-#  define ZSTD_LEGACY_SUPPORT 1
-#endif
-
-
 /* *************************************
 *  Compiler Options
 ***************************************/
@@ -29,6 +19,7 @@
 #  define _POSIX_SOURCE 1          /* disable %llu warnings with MinGW on Windows */
 #endif
 
+
 /*-*************************************
 *  Includes
 ***************************************/
@@ -44,10 +35,6 @@
 #define ZSTD_STATIC_LINKING_ONLY   /* ZSTD_magicNumber, ZSTD_frameHeaderSize_max */
 #include "zstd.h"
 
-#if defined(ZSTD_LEGACY_SUPPORT) && (ZSTD_LEGACY_SUPPORT==1)
-#  include "zstd_legacy.h"    /* ZSTD_isLegacy */
-#endif
-
 
 /*-*************************************
 *  OS-specific Includes
@@ -634,7 +621,7 @@ unsigned long long FIO_decompressFrame(dRess_t ress,
     @return : 0 (no error) */
 static unsigned FIO_passThrough(FILE* foutput, FILE* finput, void* buffer, size_t bufferSize)
 {
-    size_t const blockSize = MIN (64 KB, bufferSize);
+    size_t const blockSize = MIN(64 KB, bufferSize);
     size_t readFromInput = 1;
     unsigned storedSkips = 0;
 
@@ -682,21 +669,16 @@ static int FIO_decompressSrcFile(dRess_t ress, const char* srcFileName)
         }
         readSomething = 1;   /* there is at least >= 4 bytes in srcFile */
         if (sizeCheck != toRead) { DISPLAY("zstd: %s: unknown header \n", srcFileName); fclose(srcFile); return 1; }  /* srcFileName is empty */
-        {   U32 const magic = MEM_readLE32(ress.srcBuffer);
-            if (((magic & 0xFFFFFFF0U) != ZSTD_MAGIC_SKIPPABLE_START) & (magic != ZSTD_MAGICNUMBER)
-#if defined(ZSTD_LEGACY_SUPPORT) && (ZSTD_LEGACY_SUPPORT >= 1)
-                  & (!ZSTD_isLegacy(ress.srcBuffer, toRead))
-#endif
-                ) {
-                if ((g_overwrite) && !strcmp (srcFileName, stdinmark)) {  /* pass-through mode */
-                    unsigned const result = FIO_passThrough(dstFile, srcFile, ress.srcBuffer, ress.srcBufferSize);
-                    if (fclose(srcFile)) EXM_THROW(32, "zstd: %s close error", srcFileName);  /* error should never happen */
-                    return result;
-                } else {
-                    DISPLAYLEVEL(1, "zstd: %s: not in zstd format \n", srcFileName);
-                    fclose(srcFile);
-                    return 1;
-        }   }   }
+        if (!ZSTD_isFrame(ress.srcBuffer, toRead)) {
+            if ((g_overwrite) && !strcmp (srcFileName, stdinmark)) {  /* pass-through mode */
+                unsigned const result = FIO_passThrough(dstFile, srcFile, ress.srcBuffer, ress.srcBufferSize);
+                if (fclose(srcFile)) EXM_THROW(32, "zstd: %s close error", srcFileName);  /* error should never happen */
+                return result;
+            } else {
+                DISPLAYLEVEL(1, "zstd: %s: not in zstd format \n", srcFileName);
+                fclose(srcFile);
+                return 1;
+        }   }
         filesize += FIO_decompressFrame(ress, dstFile, srcFile, toRead);
     }