diff --git a/scrape/scrape.go b/scrape/scrape.go
index aa2d5538b1..9bff47eebc 100644
--- a/scrape/scrape.go
+++ b/scrape/scrape.go
@@ -1512,13 +1512,13 @@ func (sl *scrapeLoop) append(app storage.Appender, b []byte, contentType string,
 loop:
 	for {
 		var (
-			et                       textparse.Entry
-			sampleAdded, isHistogram bool
-			met                      []byte
-			parsedTimestamp          *int64
-			val                      float64
-			h                        *histogram.Histogram
-			fh                       *histogram.FloatHistogram
+			et                                             textparse.Entry
+			sampleAdded, isHistogram, seriesAlreadyScraped bool
+			met                                            []byte
+			parsedTimestamp                                *int64
+			val                                            float64
+			h                                              *histogram.Histogram
+			fh                                             *histogram.FloatHistogram
 		)
 		if et, err = p.Next(); err != nil {
 			if errors.Is(err, io.EOF) {
@@ -1573,6 +1573,7 @@ loop:
 		if ok {
 			ref = ce.ref
 			lset = ce.lset
+			hash = ce.hash
 
 			// Update metadata only if it changed in the current iteration.
 			updateMetadata(lset, false)
@@ -1609,24 +1610,30 @@ loop:
 			updateMetadata(lset, true)
 		}
 
-		if ctMs := p.CreatedTimestamp(); sl.enableCTZeroIngestion && ctMs != nil {
-			ref, err = app.AppendCTZeroSample(ref, lset, t, *ctMs)
-			if err != nil && !errors.Is(err, storage.ErrOutOfOrderCT) { // OOO is a common case, ignoring completely for now.
-				// CT is an experimental feature. For now, we don't need to fail the
-				// scrape on errors updating the created timestamp, log debug.
-				level.Debug(sl.l).Log("msg", "Error when appending CT in scrape loop", "series", string(met), "ct", *ctMs, "t", t, "err", err)
+		_, seriesAlreadyScraped = sl.cache.seriesCur[hash]
+		if seriesAlreadyScraped {
+			err = storage.ErrDuplicateSampleForTimestamp
+		} else {
+			if ctMs := p.CreatedTimestamp(); sl.enableCTZeroIngestion && ctMs != nil {
+				ref, err = app.AppendCTZeroSample(ref, lset, t, *ctMs)
+				if err != nil && !errors.Is(err, storage.ErrOutOfOrderCT) { // OOO is a common case, ignoring completely for now.
+					// CT is an experimental feature. For now, we don't need to fail the
+					// scrape on errors updating the created timestamp, log debug.
+					level.Debug(sl.l).Log("msg", "Error when appending CT in scrape loop", "series", string(met), "ct", *ctMs, "t", t, "err", err)
+				}
+			}
+
+			if isHistogram {
+				if h != nil {
+					ref, err = app.AppendHistogram(ref, lset, t, h, nil)
+				} else {
+					ref, err = app.AppendHistogram(ref, lset, t, nil, fh)
+				}
+			} else {
+				ref, err = app.Append(ref, lset, t, val)
 			}
 		}
 
-		if isHistogram {
-			if h != nil {
-				ref, err = app.AppendHistogram(ref, lset, t, h, nil)
-			} else {
-				ref, err = app.AppendHistogram(ref, lset, t, nil, fh)
-			}
-		} else {
-			ref, err = app.Append(ref, lset, t, val)
-		}
 		sampleAdded, err = sl.checkAddError(ce, met, parsedTimestamp, err, &sampleLimitErr, &bucketLimitErr, &appErrs)
 		if err != nil {
 			if !errors.Is(err, storage.ErrNotFound) {
@@ -1648,6 +1655,8 @@ loop:
 
 		// Increment added even if there's an error so we correctly report the
 		// number of samples remaining after relabeling.
+		// We still report duplicated samples here since this number should be the exact number
+		// of time series exposed on a scrape after relabelling.
 		added++
 		exemplars = exemplars[:0] // Reset and reuse the exemplar slice.
 		for hasExemplar := p.Exemplar(&e); hasExemplar; hasExemplar = p.Exemplar(&e) {
diff --git a/scrape/scrape_test.go b/scrape/scrape_test.go
index e37d091aec..4732fbe0d0 100644
--- a/scrape/scrape_test.go
+++ b/scrape/scrape_test.go
@@ -3600,3 +3600,31 @@ func BenchmarkTargetScraperGzip(b *testing.B) {
 		})
 	}
 }
+
+// When a scrape contains multiple instances for the same time series we should increment
+// prometheus_target_scrapes_sample_duplicate_timestamp_total metric.
+func TestScrapeLoopSeriesAddedDuplicates(t *testing.T) {
+	ctx, sl := simpleTestScrapeLoop(t)
+
+	slApp := sl.appender(ctx)
+	total, added, seriesAdded, err := sl.append(slApp, []byte("test_metric 1\ntest_metric 2\ntest_metric 3\n"), "", time.Time{})
+	require.NoError(t, err)
+	require.NoError(t, slApp.Commit())
+	require.Equal(t, 3, total)
+	require.Equal(t, 3, added)
+	require.Equal(t, 1, seriesAdded)
+
+	slApp = sl.appender(ctx)
+	total, added, seriesAdded, err = sl.append(slApp, []byte("test_metric 1\ntest_metric 1\ntest_metric 1\n"), "", time.Time{})
+	require.NoError(t, err)
+	require.NoError(t, slApp.Commit())
+	require.Equal(t, 3, total)
+	require.Equal(t, 3, added)
+	require.Equal(t, 0, seriesAdded)
+
+	metric := dto.Metric{}
+	err = sl.metrics.targetScrapeSampleDuplicate.Write(&metric)
+	require.NoError(t, err)
+	value := metric.GetCounter().GetValue()
+	require.Equal(t, 4.0, value)
+}