diff --git a/tests/testthat/test-ui-piping.R b/tests/testthat/test-ui-piping.R
index 7fc54c6e6..8337f4b16 100644
--- a/tests/testthat/test-ui-piping.R
+++ b/tests/testthat/test-ui-piping.R
@@ -1984,3 +1984,61 @@ test_that("off-diagonal piping issue #518", {
   expect_error(modNew$omega, NA)
 
 })
+
+test_that("piping append", {
+
+  mod <- function() {
+    ini({
+      tka <- 0.45
+      label("Ka")
+      tcl <- 1
+      label("Cl")
+      tv <- 3.45
+      label("V")
+      add.sd <- c(0, 0.7)
+      eta.cl ~ 0.3
+      eta.v ~ 0.1
+    })
+    model({
+      ka <- exp(tka)
+      cl <- exp(tcl + eta.cl)
+      v <- exp(tv + eta.v)
+      d/dt(depot) = -ka * depot
+      d/dt(center) = ka * depot - cl/v * center
+      cp = center/v
+      cp ~ add(add.sd)
+    })
+  }
+
+  mod5 <- mod |>
+    model({
+      PD <- 1-emax*cp/(ec50+cp)
+      ##
+      effect(0) <- e0
+      kin <- e0*kout
+      d/dt(effect) <- kin*PD -kout*effect
+    }, append=d/dt(center))
+
+  expect_equal(mod5$theta, c(tka = 0.45, tcl = 1, tv = 3.45, add.sd = 0.7))
+
+  mod6 <- mod5 |>
+    model({
+      emax <- exp(temax)
+      e0 <- exp(te0 + eta.e0)
+      ec50 <- exp(tec50)
+      kin <- exp(tkin)
+      kout <- exp(tkout)
+    }, append=NA)
+
+  expect_equal(mod6$theta,
+               c(tka = 0.45, tcl = 1, tv = 3.45, add.sd = 0.7, temax = 1, te0 = 1, tec50 = 1, tkin = 1, tkout = 1))
+
+  expect_equal(
+    mod6$omega,
+    lotri({
+      eta.cl ~ 0.3
+      eta.v ~ 0.1
+      eta.e0 ~ 1
+    }))
+
+})