diff --git a/lib/Makefile b/lib/Makefile
index a549b82bd..b6d6e25b9 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -189,7 +189,7 @@ else ifeq ($(UNAME), OpenBSD)
 endif
 HASH ?= md5sum
 
-HASH_DIR = conf_$(shell echo $(CC) $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) $(ZSTD_FILES) | $(HASH) | head -c 16)
+HASH_DIR = conf_$(shell echo $(CC) $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) $(ZSTD_FILES) | $(HASH) | cut -f 1 -d " " )
 HAVE_HASH :=$(shell echo 1 | $(HASH) > /dev/null && echo 1 || echo 0)
 ifeq ($(HAVE_HASH),0)
   $(info warning : could not find HASH ($(HASH)), needed to differentiate builds using different flags)
diff --git a/lib/compress/zstd_compress.c b/lib/compress/zstd_compress.c
index b1bb9fa10..b19b74127 100644
--- a/lib/compress/zstd_compress.c
+++ b/lib/compress/zstd_compress.c
@@ -202,6 +202,14 @@ size_t ZSTD_sizeof_CStream(const ZSTD_CStream* zcs)
 /* private API call, for dictBuilder only */
 const seqStore_t* ZSTD_getSeqStore(const ZSTD_CCtx* ctx) { return &(ctx->seqStore); }
 
+/* Returns 1 if compression parameters are such that we should
+ * enable long distance matching (wlog >= 27, strategy >= btopt).
+ * Returns 0 otherwise.
+ */
+static U32 ZSTD_CParams_shouldEnableLdm(const ZSTD_compressionParameters* const cParams) {
+    return cParams->strategy >= ZSTD_btopt && cParams->windowLog >= 27;
+}
+
 static ZSTD_CCtx_params ZSTD_makeCCtxParamsFromCParams(
         ZSTD_compressionParameters cParams)
 {
@@ -209,6 +217,16 @@ static ZSTD_CCtx_params ZSTD_makeCCtxParamsFromCParams(
     /* should not matter, as all cParams are presumed properly defined */
     ZSTD_CCtxParams_init(&cctxParams, ZSTD_CLEVEL_DEFAULT);
     cctxParams.cParams = cParams;
+
+    if (ZSTD_CParams_shouldEnableLdm(&cParams)) {
+        DEBUGLOG(4, "ZSTD_makeCCtxParamsFromCParams(): Including LDM into cctx params");
+        cctxParams.ldmParams.enableLdm = 1;
+        /* LDM is enabled by default for optimal parser and window size >= 128MB */
+        ZSTD_ldm_adjustParameters(&cctxParams.ldmParams, &cParams);
+        assert(cctxParams.ldmParams.hashLog >= cctxParams.ldmParams.bucketSizeLog);
+        assert(cctxParams.ldmParams.hashRateLog < 32);
+    }
+
     assert(!ZSTD_checkCParams(cParams));
     return cctxParams;
 }
@@ -2374,7 +2392,11 @@ static size_t ZSTD_buildSeqStore(ZSTD_CCtx* zc, const void* src, size_t srcSize)
     /* Assert that we have correctly flushed the ctx params into the ms's copy */
     ZSTD_assertEqualCParams(zc->appliedParams.cParams, ms->cParams);
     if (srcSize < MIN_CBLOCK_SIZE+ZSTD_blockHeaderSize+1) {
-        ZSTD_ldm_skipSequences(&zc->externSeqStore, srcSize, zc->appliedParams.cParams.minMatch);
+        if (zc->appliedParams.cParams.strategy >= ZSTD_btopt) {
+            ZSTD_ldm_skipRawSeqStoreBytes(&zc->externSeqStore, srcSize);
+        } else {
+            ZSTD_ldm_skipSequences(&zc->externSeqStore, srcSize, zc->appliedParams.cParams.minMatch);
+        }
         return ZSTDbss_noCompress; /* don't even attempt compression below a certain srcSize */
     }
     ZSTD_resetSeqStore(&(zc->seqStore));
@@ -2853,6 +2875,7 @@ size_t ZSTD_referenceExternalSequences(ZSTD_CCtx* cctx, rawSeq* seq, size_t nbSe
     cctx->externSeqStore.size = nbSeq;
     cctx->externSeqStore.capacity = nbSeq;
     cctx->externSeqStore.pos = 0;
+    cctx->externSeqStore.posInSequence = 0;
     return 0;
 }
 
@@ -4178,6 +4201,11 @@ size_t ZSTD_compressStream2( ZSTD_CCtx* cctx,
                     dictSize, mode);
         }
 
+        if (ZSTD_CParams_shouldEnableLdm(&params.cParams)) {
+            /* Enable LDM by default for optimal parser and window size >= 128MB */
+            DEBUGLOG(4, "LDM enabled by default (window size >= 128MB, strategy >= btopt)");
+            params.ldmParams.enableLdm = 1;
+        }
 
 #ifdef ZSTD_MULTITHREAD
         if ((cctx->pledgedSrcSizePlusOne-1) <= ZSTDMT_JOBSIZE_MIN) {
diff --git a/lib/compress/zstd_ldm.c b/lib/compress/zstd_ldm.c
index a6e780b9e..3f3d7c46a 100644
--- a/lib/compress/zstd_ldm.c
+++ b/lib/compress/zstd_ldm.c
@@ -577,10 +577,7 @@ static rawSeq maybeSplitSequence(rawSeqStore_t* rawSeqStore,
     return sequence;
 }
 
-/* ZSTD_ldm_skipRawSeqStoreBytes():
- * Moves forward in rawSeqStore by nbBytes, updating fields 'pos' and 'posInSequence'.
- */
-static void ZSTD_ldm_skipRawSeqStoreBytes(rawSeqStore_t* rawSeqStore, size_t nbBytes) {
+void ZSTD_ldm_skipRawSeqStoreBytes(rawSeqStore_t* rawSeqStore, size_t nbBytes) {
     U32 currPos = (U32)(rawSeqStore->posInSequence + nbBytes);
     while (currPos && rawSeqStore->pos < rawSeqStore->size) {
         rawSeq currSeq = rawSeqStore->seq[rawSeqStore->pos];
diff --git a/lib/compress/zstd_ldm.h b/lib/compress/zstd_ldm.h
index 229ea05a9..6561024e4 100644
--- a/lib/compress/zstd_ldm.h
+++ b/lib/compress/zstd_ldm.h
@@ -78,6 +78,12 @@ size_t ZSTD_ldm_blockCompress(rawSeqStore_t* rawSeqStore,
 void ZSTD_ldm_skipSequences(rawSeqStore_t* rawSeqStore, size_t srcSize,
     U32 const minMatch);
 
+/* ZSTD_ldm_skipRawSeqStoreBytes():
+ * Moves forward in rawSeqStore by nbBytes, updating fields 'pos' and 'posInSequence'.
+ * Not to be used in conjunction with ZSTD_ldm_skipSequences().
+ * Must be called for data with is not passed to ZSTD_ldm_blockCompress().
+ */
+void ZSTD_ldm_skipRawSeqStoreBytes(rawSeqStore_t* rawSeqStore, size_t nbBytes);
 
 /** ZSTD_ldm_getTableSize() :
  *  Estimate the space needed for long distance matching tables or 0 if LDM is
diff --git a/lib/zstd.h b/lib/zstd.h
index 75d5bb237..733595d9c 100644
--- a/lib/zstd.h
+++ b/lib/zstd.h
@@ -339,7 +339,9 @@ typedef enum {
                                      * for large inputs, by finding large matches at long distance.
                                      * It increases memory usage and window size.
                                      * Note: enabling this parameter increases default ZSTD_c_windowLog to 128 MB
-                                     * except when expressly set to a different value. */
+                                     * except when expressly set to a different value. 
+                                     * Note: will be enabled by default if ZSTD_c_windowLog >= 128 MB and
+                                     * compression strategy >= ZSTD_btopt (== compression level 16+) */
     ZSTD_c_ldmHashLog=161,   /* Size of the table for long distance matching, as a power of 2.
                               * Larger values increase memory usage and compression ratio,
                               * but decrease compression speed.
diff --git a/programs/Makefile b/programs/Makefile
index e9ba02cd5..b412e986e 100644
--- a/programs/Makefile
+++ b/programs/Makefile
@@ -110,7 +110,7 @@ else ifeq ($(UNAME), OpenBSD)
 endif
 HASH ?= md5sum
 
-HASH_DIR = conf_$(shell echo $(CC) $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) $(ZSTD_FILES) | $(HASH) | head -c 16)
+HASH_DIR = conf_$(shell echo $(CC) $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) $(ZSTD_FILES) | $(HASH) | cut -f 1 -d " ")
 HAVE_HASH :=$(shell echo 1 | $(HASH) > /dev/null && echo 1 || echo 0)
 ifeq ($(HAVE_HASH),0)
   $(info warning : could not find HASH ($(HASH)), needed to differentiate builds using different flags)
diff --git a/tests/fuzzer.c b/tests/fuzzer.c
index e54714fdf..7d1d0153d 100644
--- a/tests/fuzzer.c
+++ b/tests/fuzzer.c
@@ -1158,6 +1158,26 @@ static int basicUnitTests(U32 const seed, double compressibility)
     }
     DISPLAYLEVEL(3, "OK \n");
 
+    DISPLAYLEVEL(3, "test%3d : ldm conditionally enabled by default doesn't change cctx params: ", testNb++);
+    {   ZSTD_CCtx* const cctx = ZSTD_createCCtx();
+        ZSTD_outBuffer out = {NULL, 0, 0};
+        ZSTD_inBuffer in = {NULL, 0, 0};
+        int value;
+
+        /* Even if LDM will be enabled by default in the applied params (since wlog >= 27 and strategy >= btopt),
+         * we should not modify the actual parameter specified by the user within the CCtx
+         */
+        CHECK_Z(ZSTD_CCtx_setParameter(cctx, ZSTD_c_windowLog, 27));
+        CHECK_Z(ZSTD_CCtx_setParameter(cctx, ZSTD_c_strategy, ZSTD_btopt));
+
+        CHECK_Z(ZSTD_compressStream2(cctx, &out, &in, ZSTD_e_continue));
+        CHECK_Z(ZSTD_CCtx_getParameter(cctx, ZSTD_c_enableLongDistanceMatching, &value));
+        CHECK_EQ(value, 0);
+
+        ZSTD_freeCCtx(cctx);
+    }
+    DISPLAYLEVEL(3, "OK \n");
+
     /* this test is really too long, and should be made faster */
     DISPLAYLEVEL(3, "test%3d : overflow protection with large windowLog : ", testNb++);
     {   ZSTD_CCtx* const cctx = ZSTD_createCCtx();