diff --git a/lib/dictBuilder/fastcover.c b/lib/dictBuilder/fastcover.c
index 56a08138520..f59170ece60 100644
--- a/lib/dictBuilder/fastcover.c
+++ b/lib/dictBuilder/fastcover.c
@@ -317,10 +317,11 @@ FASTCOVER_ctx_init(FASTCOVER_ctx_t* ctx,
     const unsigned nbTestSamples = splitPoint < 1.0 ? nbSamples - nbTrainSamples : nbSamples;
     const size_t trainingSamplesSize = splitPoint < 1.0 ? COVER_sum(samplesSizes, nbTrainSamples) : totalSamplesSize;
     const size_t testSamplesSize = splitPoint < 1.0 ? COVER_sum(samplesSizes + nbTrainSamples, nbTestSamples) : totalSamplesSize;
+    const size_t readLength = MAX(d, sizeof(U64));
     ctx->displayLevel = displayLevel;
 
     /* Checks */
-    if (totalSamplesSize < MAX(d, sizeof(U64)) ||
+    if (totalSamplesSize < readLength ||
         totalSamplesSize >= (size_t)FASTCOVER_MAX_SAMPLES_SIZE) {
         DISPLAYLEVEL(1, "Total samples size is too large (%u MB), maximum size is %u MB\n",
                     (unsigned)(totalSamplesSize >> 20), (FASTCOVER_MAX_SAMPLES_SIZE >> 20));
@@ -339,6 +340,12 @@ FASTCOVER_ctx_init(FASTCOVER_ctx_t* ctx,
         return ERROR(srcSize_wrong);
     }
 
+    /* Check the training set can hold at least one dmer, otherwise nbDmers underflows below */
+    if (trainingSamplesSize < readLength) {
+        DISPLAYLEVEL(1, "Total training samples size is %u and is invalid.\n", (unsigned)trainingSamplesSize);
+        return ERROR(srcSize_wrong);
+    }
+
     /* Zero the context */
     memset(ctx, 0, sizeof(*ctx));
     DISPLAYLEVEL(2, "Training on %u samples of total size %u\n", nbTrainSamples,
@@ -351,7 +358,7 @@ FASTCOVER_ctx_init(FASTCOVER_ctx_t* ctx,
     ctx->nbSamples = nbSamples;
     ctx->nbTrainSamples = nbTrainSamples;
     ctx->nbTestSamples = nbTestSamples;
-    ctx->nbDmers = trainingSamplesSize - MAX(d, sizeof(U64)) + 1;
+    ctx->nbDmers = trainingSamplesSize - readLength + 1;
     ctx->d = d;
     ctx->f = f;
     ctx->accelParams = accelParams;
diff --git a/tests/fuzzer.c b/tests/fuzzer.c
index 7b7c9d66631..43850a9d7b5 100644
--- a/tests/fuzzer.c
+++ b/tests/fuzzer.c
@@ -3060,6 +3060,16 @@ static int basicUnitTests(U32 const seed, double compressibility)
         if (ZDICT_isError(dictSize)) goto _output_error;
         DISPLAYLEVEL(3, "OK, created dictionary of size %u \n", (unsigned)dictSize);
 
+        DISPLAYLEVEL(3, "test%3i : FASTCOVER dictBuilder samples smaller than a dmer (issue #4499) : ", testNb++);
+        {   const char smallData[8] = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H' };
+            const size_t smallSizes[8] = { 1, 1, 1, 1, 1, 1, 1, 1 };
+            size_t const r = ZDICT_trainFromBuffer(dictBuffer, dictBufferCapacity,
+                                                   smallData, smallSizes, 8);
+            if (!ZDICT_isError(r)) goto _output_error;
+            if (ZSTD_getErrorCode(r) != ZSTD_error_srcSize_wrong) goto _output_error;
+        }
+        DISPLAYLEVEL(3, "OK \n");
+
         DISPLAYLEVEL(3, "test%3i : Multithreaded COVER dictBuilder : ", testNb++);
         { U32 u; for (u=0; u<nbSamples; u++) samplesSizes[u] = sampleUnitSize; }
         {   ZDICT_cover_params_t coverParams;