diff --git a/lib/compress/zstd_ldm.c b/lib/compress/zstd_ldm.c
index 341877858..356549f36 100644
--- a/lib/compress/zstd_ldm.c
+++ b/lib/compress/zstd_ldm.c
@@ -575,6 +575,8 @@ size_t ZSTD_ldm_blockCompress(rawSeqStore_t* rawSeqStore,
     BYTE const* const iend = istart + srcSize;
     /* Input positions */
     BYTE const* ip = istart;
+
+    /* If using opt parser, use LDMs only as candidates rather than always accepting them */
     if (cParams->strategy >= ZSTD_btopt) {
         size_t lastLLSize;
         ms->ldmSeqStore = *rawSeqStore;
diff --git a/lib/compress/zstd_opt.c b/lib/compress/zstd_opt.c
index fa3587bed..5211fc917 100644
--- a/lib/compress/zstd_opt.c
+++ b/lib/compress/zstd_opt.c
@@ -774,7 +774,9 @@ FORCE_INLINE_TEMPLATE U32 ZSTD_BtGetAllMatches (
 static void ZSTD_opt_skipBytesInLdmSeqStore(rawSeqStore_t* ldmSeqStore, size_t nbBytes) {
     while (nbBytes && ldmSeqStore->pos < ldmSeqStore->size) {
         rawSeq currSeq = ldmSeqStore->seq[ldmSeqStore->pos];
+        /* posInSequence necessarily must never represent a value beyond the sequence */
         assert(ldmSeqStore->posInSequence <= currSeq.matchLength + currSeq.litLength);
+
         if (nbBytes <= currSeq.litLength) {
             ldmSeqStore->posInSequence += nbBytes;
             return;
@@ -782,6 +784,7 @@ static void ZSTD_opt_skipBytesInLdmSeqStore(rawSeqStore_t* ldmSeqStore, size_t n
             ldmSeqStore->posInSequence += currSeq.litLength;
             nbBytes -= currSeq.litLength;
         }
+        
         if (nbBytes < currSeq.matchLength) {
             ldmSeqStore->posInSequence += nbBytes;
             return;
diff --git a/tests/fuzzer.c b/tests/fuzzer.c
index 8b10078ac..82d2f119e 100644
--- a/tests/fuzzer.c
+++ b/tests/fuzzer.c
@@ -780,6 +780,44 @@ static int basicUnitTests(U32 const seed, double compressibility)
     }
     DISPLAYLEVEL(3, "OK \n");
 
+    DISPLAYLEVEL(3, "test%3i : testing ldm no regressions in size for opt parser : ", testNb++);
+    {
+        size_t cSizeLdm;
+        size_t cSizeNoLdm;
+        ZSTD_CCtx* const cctx = ZSTD_createCCtx();
+
+        RDG_genBuffer(CNBuffer, CNBuffSize, 0.5, 0.5, seed);
+
+        /* Enable checksum to verify round trip. */
+        CHECK_Z(ZSTD_CCtx_setParameter(cctx, ZSTD_c_checksumFlag, 1));
+        CHECK_Z(ZSTD_CCtx_setParameter(cctx, ZSTD_c_enableLongDistanceMatching, 1));
+        CHECK_Z(ZSTD_CCtx_setParameter(cctx, ZSTD_c_compressionLevel, 19));
+
+        /* Round trip once with ldm. */
+        cSizeLdm = ZSTD_compress2(cctx, compressedBuffer, compressedBufferSize, CNBuffer, CNBuffSize);
+        CHECK_Z(cSizeLdm);
+        CHECK_Z(ZSTD_decompress(decodedBuffer, CNBuffSize, compressedBuffer, cSizeLdm));
+
+        ZSTD_CCtx_reset(cctx, ZSTD_reset_session_and_parameters);
+        CHECK_Z(ZSTD_CCtx_setParameter(cctx, ZSTD_c_checksumFlag, 1));
+        CHECK_Z(ZSTD_CCtx_setParameter(cctx, ZSTD_c_enableLongDistanceMatching, 0));
+        CHECK_Z(ZSTD_CCtx_setParameter(cctx, ZSTD_c_compressionLevel, 19));
+
+        /* Round trip once without ldm. */
+        cSizeNoLdm = ZSTD_compress2(cctx, compressedBuffer, compressedBufferSize, CNBuffer, CNBuffSize);
+        CHECK_Z(cSizeNoLdm);
+        CHECK_Z(ZSTD_decompress(decodedBuffer, CNBuffSize, compressedBuffer, cSizeNoLdm));
+
+        if (cSizeLdm > cSizeNoLdm) {
+            DISPLAY("Using long mode should not cause regressions for btopt+\n");
+            testResult = 1;
+            goto _output_error;
+        }
+
+        ZSTD_freeCCtx(cctx);
+    }
+    DISPLAYLEVEL(3, "OK \n");
+
     /* Note: this test takes 0.5 seconds to run */
     DISPLAYLEVEL(3, "test%3i : testing refPrefx vs refPrefx + ldm (size comparison) : ", testNb++);
     {
diff --git a/tests/playTests.sh b/tests/playTests.sh
index 3959a8f3a..49371040e 100755
--- a/tests/playTests.sh
+++ b/tests/playTests.sh
@@ -1217,7 +1217,7 @@ then
     println "\n===>  zstdmt round-trip tests "
     roundTripTest -g4M "1 -T0"
     roundTripTest -g8M "3 -T2"
-    roundTripTest -g8M "3 -T0 --long"
+    roundTripTest -g8M "19 -T0 --long"
     roundTripTest -g8000K "2 --threads=2"
     fileRoundTripTest -g4M "19 -T2 -B1M"