diff --git a/lib/common/compiler.h b/lib/common/compiler.h
index b588e110..366ed2b4 100644
--- a/lib/common/compiler.h
+++ b/lib/common/compiler.h
@@ -92,7 +92,7 @@
 #if defined(_MSC_VER) && (defined(_M_X64) || defined(_M_I86))  /* _mm_prefetch() is not defined outside of x86/x64 */
 #  include <mmintrin.h>   /* https://msdn.microsoft.com/fr-fr/library/84szxsww(v=vs.90).aspx */
 #  define PREFETCH(ptr)   _mm_prefetch((const char*)ptr, _MM_HINT_T0)
-#elif defined(__GNUC__)
+#elif defined(__GNUC__) && ( (__GNUC__ >= 4) || ( (__GNUC__ == 3) && (__GNUC_MINOR__ >= 1) ) )
 #  define PREFETCH(ptr)   __builtin_prefetch(ptr, 0, 0)
 #else
 #  define PREFETCH(ptr)   /* disabled */
diff --git a/lib/common/cpu.h b/lib/common/cpu.h
index 4eb48e39..88e0ebf4 100644
--- a/lib/common/cpu.h
+++ b/lib/common/cpu.h
@@ -72,8 +72,7 @@ MEM_STATIC ZSTD_cpuid_t ZSTD_cpuid(void) {
           "cpuid\n\t"
           "popl %%ebx\n\t"
           : "=a"(f1a), "=c"(f1c), "=d"(f1d)
-          : "a"(1)
-          :);
+          : "a"(1));
     }
     if (n >= 7) {
       __asm__(
diff --git a/lib/compress/zstd_opt.c b/lib/compress/zstd_opt.c
index 03c5b5b6..b72eea69 100644
--- a/lib/compress/zstd_opt.c
+++ b/lib/compress/zstd_opt.c
@@ -97,7 +97,7 @@ static void ZSTD_rescaleFreqs(optState_t* const optPtr,
                 for (lit=0; lit<=MaxLit; lit++) {
                     U32 const scaleLog = 11;   /* scale to 2K */
                     U32 const bitCost = HUF_getNbBits(optPtr->symbolCosts->hufCTable, lit);
-                    assert(bitCost < scaleLog);
+                    assert(bitCost <= scaleLog);
                     optPtr->litFreq[lit] = bitCost ? 1 << (scaleLog-bitCost) : 1 /*minimum to calculate cost*/;
                     optPtr->litSum += optPtr->litFreq[lit];
             }   }
diff --git a/lib/decompress/zstd_decompress.c b/lib/decompress/zstd_decompress.c
index 103dcc64..32a21308 100644
--- a/lib/decompress/zstd_decompress.c
+++ b/lib/decompress/zstd_decompress.c
@@ -1882,6 +1882,7 @@ static size_t ZSTD_decompressMultiFrame(ZSTD_DCtx* dctx,
                                   const ZSTD_DDict* ddict)
 {
     void* const dststart = dst;
+    int moreThan1Frame = 0;
     assert(dict==NULL || ddict==NULL);  /* either dict or ddict set, not both */
 
     if (ddict) {
@@ -1890,7 +1891,6 @@ static size_t ZSTD_decompressMultiFrame(ZSTD_DCtx* dctx,
     }
 
     while (srcSize >= ZSTD_frameHeaderSize_prefix) {
-        U32 magicNumber;
 
 #if defined(ZSTD_LEGACY_SUPPORT) && (ZSTD_LEGACY_SUPPORT >= 1)
         if (ZSTD_isLegacy(src, srcSize)) {
@@ -1912,10 +1912,9 @@ static size_t ZSTD_decompressMultiFrame(ZSTD_DCtx* dctx,
         }
 #endif
 
-        magicNumber = MEM_readLE32(src);
-        DEBUGLOG(4, "reading magic number %08X (expecting %08X)",
-                    (U32)magicNumber, (U32)ZSTD_MAGICNUMBER);
-        if (magicNumber != ZSTD_MAGICNUMBER) {
+        {   U32 const magicNumber = MEM_readLE32(src);
+            DEBUGLOG(4, "reading magic number %08X (expecting %08X)",
+                        (U32)magicNumber, (U32)ZSTD_MAGICNUMBER);
             if ((magicNumber & 0xFFFFFFF0U) == ZSTD_MAGIC_SKIPPABLE_START) {
                 size_t skippableSize;
                 if (srcSize < ZSTD_skippableHeaderSize)
@@ -1927,9 +1926,7 @@ static size_t ZSTD_decompressMultiFrame(ZSTD_DCtx* dctx,
                 src = (const BYTE *)src + skippableSize;
                 srcSize -= skippableSize;
                 continue;
-            }
-            return ERROR(prefix_unknown);
-        }
+        }   }
 
         if (ddict) {
             /* we were called from ZSTD_decompress_usingDDict */
@@ -1943,11 +1940,25 @@ static size_t ZSTD_decompressMultiFrame(ZSTD_DCtx* dctx,
 
         {   const size_t res = ZSTD_decompressFrame(dctx, dst, dstCapacity,
                                                     &src, &srcSize);
+            if ( (ZSTD_getErrorCode(res) == ZSTD_error_prefix_unknown)
+              && (moreThan1Frame==1) ) {
+                /* at least one frame successfully completed,
+                 * but following bytes are garbage :
+                 * it's more likely to be a srcSize error,
+                 * specifying more bytes than compressed size of frame(s).
+                 * This error message replaces ERROR(prefix_unknown),
+                 * which would be confusing, as the first header is actually correct.
+                 * Note that one could be unlucky, it might be a corruption error instead,
+                 * happening right at the place where we expect zstd magic bytes.
+                 * But this is _much_ less likely than a srcSize field error. */
+                return ERROR(srcSize_wrong);
+            }
             if (ZSTD_isError(res)) return res;
             /* no need to bound check, ZSTD_decompressFrame already has */
             dst = (BYTE*)dst + res;
             dstCapacity -= res;
         }
+        moreThan1Frame = 1;
     }  /* while (srcSize >= ZSTD_frameHeaderSize_prefix) */
 
     if (srcSize) return ERROR(srcSize_wrong); /* input not entirely consumed */
diff --git a/tests/fuzzer.c b/tests/fuzzer.c
index f9ea209f..b0c425e1 100644
--- a/tests/fuzzer.c
+++ b/tests/fuzzer.c
@@ -375,6 +375,12 @@ static int basicUnitTests(U32 seed, double compressibility)
       if (ZSTD_getErrorCode(r) != ZSTD_error_srcSize_wrong) goto _output_error; }
     DISPLAYLEVEL(3, "OK \n");
 
+    DISPLAYLEVEL(3, "test%3i : decompress too large input : ", testNb++);
+    { size_t const r = ZSTD_decompress(decodedBuffer, CNBuffSize, compressedBuffer, compressedBufferSize);
+      if (!ZSTD_isError(r)) goto _output_error;
+      if (ZSTD_getErrorCode(r) != ZSTD_error_srcSize_wrong) goto _output_error; }
+    DISPLAYLEVEL(3, "OK \n");
+
     DISPLAYLEVEL(3, "test%3d : check CCtx size after compressing empty input : ", testNb++);
     {   ZSTD_CCtx* cctx = ZSTD_createCCtx();
         size_t const r = ZSTD_compressCCtx(cctx, compressedBuffer, compressedBufferSize, NULL, 0, 19);