diff --git a/R/g_lineplot.R b/R/g_lineplot.R
index 3347e9e726..e7bfebc28b 100644
--- a/R/g_lineplot.R
+++ b/R/g_lineplot.R
@@ -216,7 +216,7 @@ g_lineplot <- function(df, # nolint
     df_grp <- tidyr::expand(df, NULL, .data[[x]])
   }
   df_grp <- df_grp %>%
-    dplyr::full_join(y = df[, c(strata, x, y)], by = c(strata, x)) %>%
+    dplyr::full_join(y = df[, c(strata, x, y)], by = c(strata, x), multiple = "all") %>%
     dplyr::group_by_at(c(strata, x))
 
   df_stats <- df_grp %>%
diff --git a/tests/testthat/test-g_lineplot.R b/tests/testthat/test-g_lineplot.R
new file mode 100644
index 0000000000..7091cd11d1
--- /dev/null
+++ b/tests/testthat/test-g_lineplot.R
@@ -0,0 +1,23 @@
+adsl <- tern_ex_adsl
+adlb <- tern_ex_adlb %>% dplyr::filter(ANL01FL == "Y", PARAMCD == "ALT", AVISIT != "SCREENING")
+adlb$AVISIT <- droplevels(adlb$AVISIT)
+adlb <- dplyr::mutate(adlb, AVISIT = forcats::fct_reorder(AVISIT, AVISITN, min))
+
+testthat::test_that("g_lineplot works with default settings", {
+  testthat::expect_silent(g_lineplot(adlb, adsl))
+})
+
+testthat::test_that("g_lineplot works with custom settings and statistics table", {
+  testthat::expect_silent(g_lineplot(
+    adlb,
+    adsl,
+    strata = control_lineplot_vars(strata = NULL),
+    mid = "median",
+    table = c("n", "mean", "mean_ci"),
+    control = control_summarize_vars(conf_level = 0.80),
+    title = "Plot of Mean and 80% Confidence Limits by Visit",
+    y_lab = "Lab Test",
+    subtitle = "Laboratory Test:",
+    caption = "caption"
+  ))
+})