diff --git a/R/typst_style.R b/R/typst_style.R
index 53bcf98f0..0310396d6 100644
--- a/R/typst_style.R
+++ b/R/typst_style.R
@@ -240,6 +240,14 @@ typst_hlines <- function(x, lin) {
   tmp <- split(lin, list(lin$i, lin$line, lin$line_color_mapped, lin$line_width))
   tmp <- Filter(function(x) nrow(x) > 0, tmp)
   tmp <- lapply(tmp, function(k) {
+    # Drop duplicate cell-level entries. These arise routinely whenever
+    # theme_tinytable() and a user style_tt() declare the same line (same
+    # i, j, line, color, width, trim). Without deduplication,
+    # typst_split_chunks() sees phantom breaks in diff(x) != 1 and emits a
+    # chain of fragmented table.hline()/table.vline() segments that cover
+    # the same span as a single line. See test-typst-line-dedup.R.
+    k <- k[!duplicated(k), , drop = FALSE]
+
     # Split chunks based on consecutive columns AND line_trim boundaries
     # line_trim marks group boundaries - split chunks at these points
     chunks <- typst_split_chunks(k$j)
@@ -462,6 +470,8 @@ typst_vlines <- function(x, lin) {
   lin <- split(lin, list(lin$j, lin$line, lin$line_color_mapped, lin$line_width))
   lin <- Filter(function(x) nrow(x) > 0, lin)
   lin <- lapply(lin, function(k) {
+    # Drop duplicate cell-level entries; see typst_hlines() for rationale.
+    k <- k[!duplicated(k), , drop = FALSE]
     ymin <- typst_split_chunks(k$i)$min
     ymax <- typst_split_chunks(k$i)$max
     xmin <- k$j[1]
diff --git a/inst/tinytest/_tinysnapshot/typst-issue592.typ b/inst/tinytest/_tinysnapshot/typst-issue592.typ
index ba40cf261..b4d19daec 100644
--- a/inst/tinytest/_tinysnapshot/typst-issue592.typ
+++ b/inst/tinytest/_tinysnapshot/typst-issue592.typ
@@ -78,11 +78,7 @@ block[ // start block
  table.hline(y: 14, start: 1, end: 2, stroke: 0.1em + black), table.hline(y: 14, start: 3, end: 7, stroke: 0.1em + black),
  table.hline(y: 15, start: 1, end: 2, stroke: 0.1em + black), table.hline(y: 15, start: 3, end: 7, stroke: 0.1em + black),
  table.hline(y: 16, start: 2, end: 3, stroke: 0.1em + black),
- table.vline(x: 0, start: 0, end: 1, stroke: 0.1em + black),
- table.vline(x: 0, start: 0, end: 2, stroke: 0.1em + black),
- table.vline(x: 0, start: 1, end: 7, stroke: 0.1em + black),
- table.vline(x: 0, start: 6, end: 12, stroke: 0.1em + black),
- table.vline(x: 0, start: 11, end: 16, stroke: 0.1em + black),
+ table.vline(x: 0, start: 0, end: 16, stroke: 0.1em + black),
  table.vline(x: 1, start: 0, end: 16, stroke: 0.1em + black),
  table.vline(x: 2, start: 0, end: 1, stroke: 0.1em + black),
  table.vline(x: 3, start: 0, end: 1, stroke: 0.1em + black),
@@ -129,4 +125,4 @@ table.cell(rowspan: 3)[3], [x], [80.9%], [78.4%], [ ], [55.6%],
   // tinytable align-figure after
 
 ] // end block
-) // end figure 
+) // end figure 
\ No newline at end of file
diff --git a/inst/tinytest/test-bugfix.R b/inst/tinytest/test-bugfix.R
index 7478049b3..907556306 100644
--- a/inst/tinytest/test-bugfix.R
+++ b/inst/tinytest/test-bugfix.R
@@ -58,3 +58,36 @@ local({
   expect_true(grepl("1,23", typst, fixed = TRUE))
   expect_true(grepl("1,23", tabulator, fixed = TRUE))
 })
+
+
+# Regression test: typst_hlines/typst_vlines used to emit fragmented chains of
+# table.hline()/table.vline() segments covering the same span whenever
+# theme_tinytable() and the user declared the same line (or any line was
+# declared twice with identical properties). This produced redundant, ugly
+# output and slowed down rendering. The fix deduplicates cell-level entries
+# inside the typst line processors.
+
+# Case 1: user re-declares the theme's middle "below colnames" line.
+# Before the fix this produced 6 fragmented hline segments at y=1.
+tab <- tt(mtcars[1:5, 1:5]) |>
+  style_tt(i = 0, line = "b", line_color = "black", line_width = 0.05)
+out <- save_tt(tab, "typst")
+hlines <- strsplit(out, "\n", fixed = TRUE)[[1]]
+hlines <- hlines[grepl("table.hline", hlines, fixed = TRUE)]
+middle <- hlines[grepl("y: 1,", hlines, fixed = TRUE)]
+expect_true(length(middle) >= 1)
+# The whole row should contain exactly one table.hline(y: 1, ...) segment
+n_middle_segments <- lengths(regmatches(middle, gregexpr("table[.]hline", middle)))
+expect_true(n_middle_segments == 1)
+
+# Case 2: user adds the same line twice -> should still produce a single segment
+tab <- tt(mtcars[1:5, 1:5]) |>
+  style_tt(i = 2, line = "b", line_color = "pink") |>
+  style_tt(i = 2, line = "b", line_color = "pink")
+out <- save_tt(tab, "typst")
+hlines <- strsplit(out, "\n", fixed = TRUE)[[1]]
+hlines <- hlines[grepl("table.hline", hlines, fixed = TRUE)]
+dup <- hlines[grepl("y: 3,", hlines, fixed = TRUE)]
+expect_true(length(dup) >= 1)
+n_dup_segments <- lengths(regmatches(dup, gregexpr("table[.]hline", dup)))
+expect_true(n_dup_segments == 1)