diff --git a/docs/news.rst b/docs/news.rst
index 83641a75..ba9bc3b4 100644
--- a/docs/news.rst
+++ b/docs/news.rst
@@ -7,6 +7,11 @@ Version History
 next (not yet released)
 =======================
 
+* Backported `zstd's LDM size-estimation fix
+  <https://github.com/facebook/zstd/commit/81cf153bce7c0ab41aeef574a70e32eaea7a8ba7>`_
+  so ``estimated_compression_context_size()`` resolves default LDM parameters
+  instead of dividing by zero when ``enable_ldm=True``. (#345)
+
 Backwards Compatibility Notes
 -----------------------------
 
diff --git a/tests/test_data_structures.py b/tests/test_data_structures.py
index 9eaa349e..26f97e43 100644
--- a/tests/test_data_structures.py
+++ b/tests/test_data_structures.py
@@ -105,6 +105,50 @@ def test_estimated_compression_context_size(self):
             p.estimated_compression_context_size(), 1303304, delta=4000
         )
 
+    def test_estimated_compression_context_size_ldm(self):
+        # Resolved LDM defaults for a 1 MiB window, including a hash-log
+        # override and a strategy with a different default match length.
+        cases = [
+            (zstd.STRATEGY_DFAST, {}, (13, 64, 4, 7)),
+            (zstd.STRATEGY_DFAST, {"ldm_hash_log": 16}, (16, 64, 4, 4)),
+            (zstd.STRATEGY_BTULTRA2, {}, (16, 32, 8, 4)),
+        ]
+        names = (
+            "ldm_hash_log",
+            "ldm_min_match",
+            "ldm_bucket_size_log",
+            "ldm_hash_rate_log",
+        )
+
+        for strategy, overrides, defaults in cases:
+            with self.subTest(strategy=strategy, overrides=overrides):
+                kwargs = {"window_log": 20, "strategy": strategy}
+                params = zstd.ZstdCompressionParameters.from_level(
+                    3, enable_ldm=True, **kwargs, **overrides
+                )
+                explicit = zstd.ZstdCompressionParameters.from_level(
+                    3, enable_ldm=True, **kwargs, **dict(zip(names, defaults))
+                )
+                disabled = zstd.ZstdCompressionParameters.from_level(
+                    3, enable_ldm=False, **kwargs
+                )
+                before = tuple(getattr(params, name) for name in names)
+
+                size = params.estimated_compression_context_size()
+                self.assertEqual(
+                    size, explicit.estimated_compression_context_size()
+                )
+                self.assertGreater(
+                    size, disabled.estimated_compression_context_size()
+                )
+                self.assertEqual(
+                    tuple(getattr(params, name) for name in names), before
+                )
+                self.assertEqual(params.enable_ldm, 1)
+                self.assertEqual(
+                    params.estimated_compression_context_size(), size
+                )
+
     def test_strategy(self):
         p = zstd.ZstdCompressionParameters(strategy=2)
         self.assertEqual(p.strategy, 2)
diff --git a/zstd/zstd.c b/zstd/zstd.c
index cdc5194e..8ea6f6db 100644
--- a/zstd/zstd.c
+++ b/zstd/zstd.c
@@ -24709,15 +24709,19 @@ size_t ZSTD_estimateCCtxSize_usingCCtxParams(const ZSTD_CCtx_params* params)
 {
     ZSTD_compressionParameters const cParams =
                 ZSTD_getCParamsFromCCtxParams(params, ZSTD_CONTENTSIZE_UNKNOWN, 0, ZSTD_cpm_noAttachDict);
+    ldmParams_t ldmParams = params->ldmParams;
     ZSTD_ParamSwitch_e const useRowMatchFinder = ZSTD_resolveRowMatchFinderMode(params->useRowMatchFinder,
                                                                                &cParams);
 
     RETURN_ERROR_IF(params->nbWorkers > 0, GENERIC, "Estimate CCtx size is supported for single-threaded compression only.");
+    if (ldmParams.enableLdm == ZSTD_ps_enable) {
+        ZSTD_ldm_adjustParameters(&ldmParams, &cParams);
+    }
     /* estimateCCtxSize is for one-shot compression. So no buffers should
      * be needed. However, we still allocate two 0-sized buffers, which can
      * take space under ASAN. */
     return ZSTD_estimateCCtxSize_usingCCtxParams_internal(
-        &cParams, &params->ldmParams, 1, useRowMatchFinder, 0, 0, ZSTD_CONTENTSIZE_UNKNOWN, ZSTD_hasExtSeqProd(params), params->maxBlockSize);
+        &cParams, &ldmParams, 1, useRowMatchFinder, 0, 0, ZSTD_CONTENTSIZE_UNKNOWN, ZSTD_hasExtSeqProd(params), params->maxBlockSize);
 }
 
 size_t ZSTD_estimateCCtxSize_usingCParams(ZSTD_compressionParameters cParams)
@@ -24767,6 +24771,7 @@ size_t ZSTD_estimateCStreamSize_usingCCtxParams(const ZSTD_CCtx_params* params)
     RETURN_ERROR_IF(params->nbWorkers > 0, GENERIC, "Estimate CCtx size is supported for single-threaded compression only.");
     {   ZSTD_compressionParameters const cParams =
                 ZSTD_getCParamsFromCCtxParams(params, ZSTD_CONTENTSIZE_UNKNOWN, 0, ZSTD_cpm_noAttachDict);
+        ldmParams_t ldmParams = params->ldmParams;
         size_t const blockSize = MIN(ZSTD_resolveMaxBlockSize(params->maxBlockSize), (size_t)1 << cParams.windowLog);
         size_t const inBuffSize = (params->inBufferMode == ZSTD_bm_buffered)
                 ? ((size_t)1 << cParams.windowLog) + blockSize
@@ -24776,8 +24781,11 @@ size_t ZSTD_estimateCStreamSize_usingCCtxParams(const ZSTD_CCtx_params* params)
                 : 0;
         ZSTD_ParamSwitch_e const useRowMatchFinder = ZSTD_resolveRowMatchFinderMode(params->useRowMatchFinder, &params->cParams);
 
+        if (ldmParams.enableLdm == ZSTD_ps_enable) {
+            ZSTD_ldm_adjustParameters(&ldmParams, &cParams);
+        }
         return ZSTD_estimateCCtxSize_usingCCtxParams_internal(
-            &cParams, &params->ldmParams, 1, useRowMatchFinder, inBuffSize, outBuffSize,
+            &cParams, &ldmParams, 1, useRowMatchFinder, inBuffSize, outBuffSize,
             ZSTD_CONTENTSIZE_UNKNOWN, ZSTD_hasExtSeqProd(params), params->maxBlockSize);
     }
 }