diff --git a/cmd/pipe_test.go b/cmd/pipe_test.go
index bb982e28..4f8696ae 100644
--- a/cmd/pipe_test.go
+++ b/cmd/pipe_test.go
@@ -7,6 +7,7 @@ import (
 	"os"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/dropbox/dropbox-sdk-go-unofficial/v6/dropbox"
 	"github.com/dropbox/dropbox-sdk-go-unofficial/v6/dropbox/files"
@@ -112,6 +113,50 @@ func TestPutStdin_UploadsContent(t *testing.T) {
 	}
 }
 
+func TestPutStdinSetsClientModified(t *testing.T) {
+	content := "hello from stdin"
+	cmd := testPutCmdWithStdin(strings.NewReader(content))
+
+	start := time.Now().UTC()
+	var uploadedClientModified *dropbox.DBXTime
+	mock := &mockFilesClient{
+		getMetadataFn: func(arg *files.GetMetadataArg) (files.IsMetadata, error) {
+			return nil, &files.GetMetadataAPIError{}
+		},
+		uploadFn: func(arg *files.UploadArg, r io.Reader) (*files.FileMetadata, error) {
+			uploadedClientModified = arg.ClientModified
+			data, err := io.ReadAll(r)
+			if err != nil {
+				t.Fatal(err)
+			}
+			if string(data) != content {
+				t.Fatalf("uploaded content = %q, want %q", string(data), content)
+			}
+			return &files.FileMetadata{}, nil
+		},
+	}
+	stubFilesClient(t, mock)
+
+	err := put(cmd, []string{"-", "/dest.txt"})
+	end := time.Now().UTC()
+	if err != nil {
+		t.Fatalf("put stdin error: %v", err)
+	}
+	if uploadedClientModified == nil {
+		t.Fatal("ClientModified = nil, want stdin spool modified time")
+	}
+
+	got := time.Time(*uploadedClientModified)
+	lower := start.Add(-time.Second)
+	upper := end.Add(time.Second)
+	if got.Before(lower) || got.After(upper) {
+		t.Fatalf("ClientModified = %s, want between %s and %s", got.Format(time.RFC3339Nano), lower.Format(time.RFC3339Nano), upper.Format(time.RFC3339Nano))
+	}
+	if got.Location() != time.UTC {
+		t.Fatalf("ClientModified location = %v, want UTC", got.Location())
+	}
+}
+
 func TestPutStdinIfExistsSkipDoesNotReadStdin(t *testing.T) {
 	cmd := testPutCmdWithStdin(failReadReader{t: t})
 	_ = cmd.Flags().Set("if-exists", "skip")
diff --git a/cmd/put.go b/cmd/put.go
index e3ba5672..49dfc783 100644
--- a/cmd/put.go
+++ b/cmd/put.go
@@ -506,6 +506,12 @@ func putFile(src, dst string, opts putOptions) error {
 	return err
 }
 
+// Dropbox upload commit timestamps must be UTC with second precision.
+func dropboxClientModified(value time.Time) *dropbox.DBXTime {
+	ts := dropbox.DBXTime(value.UTC().Round(time.Second))
+	return &ts
+}
+
 func putFileWithResult(src, dst string, opts putOptions) (putResult, error) {
 	ifExists, err := normalizePutIfExists(opts.ifExists)
 	if err != nil {
@@ -537,9 +543,7 @@ func putFileWithResult(src, dst string, opts putOptions) (putResult, error) {
 	commitInfo.Mode.Tag = writeModeForIfExists(ifExists)
 	commitInfo.StrictConflict = ifExists != putIfExistsOverwrite
 
-	// The Dropbox API only accepts timestamps in UTC with second precision.
-	ts := dropbox.DBXTime(time.Now().UTC().Round(time.Second))
-	commitInfo.ClientModified = &ts
+	commitInfo.ClientModified = dropboxClientModified(contentsInfo.ModTime())
 
 	if contentsInfo.Size() > singleShotUploadSizeCutoff {
 		metadata, err := uploadChunked(dbx, uploadProgressReader(contents, contentsInfo.Size(), putErrorOutput(opts)), commitInfo, contentsInfo.Size(), opts.workers, opts.chunkSize, opts.debug)
diff --git a/cmd/put_test.go b/cmd/put_test.go
index db53b587..c19c95f8 100644
--- a/cmd/put_test.go
+++ b/cmd/put_test.go
@@ -1118,6 +1118,64 @@ func TestPutTextModeWritesNoStdoutOnSuccess(t *testing.T) {
 	}
 }
 
+func TestDropboxClientModifiedUsesUTCSecondPrecision(t *testing.T) {
+	input := time.Date(2026, 7, 1, 12, 34, 56, 600*1e6, time.FixedZone("source", -7*60*60))
+
+	got := dropboxClientModified(input)
+	if got == nil {
+		t.Fatal("dropboxClientModified returned nil")
+	}
+
+	gotTime := time.Time(*got)
+	want := input.UTC().Round(time.Second)
+	if !gotTime.Equal(want) {
+		t.Fatalf("client modified = %s, want %s", gotTime.Format(time.RFC3339Nano), want.Format(time.RFC3339Nano))
+	}
+	if gotTime.Location() != time.UTC {
+		t.Fatalf("client modified location = %v, want UTC", gotTime.Location())
+	}
+}
+
+func TestPutFileUsesSourceModifiedTime(t *testing.T) {
+	tmpFile := filepath.Join(t.TempDir(), "mtime.txt")
+	if err := os.WriteFile(tmpFile, []byte("test"), 0644); err != nil {
+		t.Fatal(err)
+	}
+	sourceModTime := time.Date(2020, 4, 23, 14, 37, 4, 0, time.FixedZone("source", -7*60*60))
+	if err := os.Chtimes(tmpFile, sourceModTime, sourceModTime); err != nil {
+		t.Fatal(err)
+	}
+
+	var uploadedClientModified *dropbox.DBXTime
+	mock := &mockFilesClient{
+		uploadFn: func(arg *files.UploadArg, content io.Reader) (*files.FileMetadata, error) {
+			uploadedClientModified = arg.ClientModified
+			if _, err := io.ReadAll(content); err != nil {
+				t.Fatal(err)
+			}
+			return &files.FileMetadata{}, nil
+		},
+	}
+	stubFilesClient(t, mock)
+
+	if err := putFile(tmpFile, "/mtime.txt", putOptions{
+		chunkSize: 1 << 24,
+		workers:   4,
+		ifExists:  putIfExistsOverwrite,
+	}); err != nil {
+		t.Fatalf("putFile error: %v", err)
+	}
+
+	if uploadedClientModified == nil {
+		t.Fatal("ClientModified = nil, want source file modified time")
+	}
+	got := time.Time(*uploadedClientModified)
+	want := sourceModTime.UTC().Round(time.Second)
+	if !got.Equal(want) {
+		t.Fatalf("ClientModified = %s, want %s", got.Format(time.RFC3339Nano), want.Format(time.RFC3339Nano))
+	}
+}
+
 func TestPutFileIfExistsSkipSkipsExistingFile(t *testing.T) {
 	tmpFile := filepath.Join(t.TempDir(), "test.txt")
 	if err := os.WriteFile(tmpFile, []byte("test"), 0644); err != nil {