diff --git a/R/sub.R b/R/sub.R
index 60897594..72f06b55 100644
--- a/R/sub.R
+++ b/R/sub.R
@@ -84,11 +84,13 @@ str_sub <- function(string, start = 1L, end = -1L) {
     value = value
   )
 
+  nms <- names(string)
   if (is.matrix(start)) {
     stri_sub(string, from = start, omit_na = omit_na) <- value
   } else {
     stri_sub(string, from = start, to = end, omit_na = omit_na) <- value
   }
+  names(string) <- nms
   string
 }
 
diff --git a/tests/testthat/test-case.R b/tests/testthat/test-case.R
index cdc733e0..f55b5d41 100644
--- a/tests/testthat/test-case.R
+++ b/tests/testthat/test-case.R
@@ -20,6 +20,14 @@ test_that("case conversions preserve names", {
   expect_equal(names(str_to_title(x)), names(x))
 })
 
+test_that("programming case conversions preserve names", {
+  x <- c(A = "hello-world", B = "foo-bar")
+  expect_equal(names(str_to_camel(x)), names(x))
+  expect_equal(names(str_to_camel(x, first_upper = TRUE)), names(x))
+  expect_equal(names(str_to_snake(c(A = "helloWorld", B = "fooBar"))), c("A", "B"))
+  expect_equal(names(str_to_kebab(c(A = "helloWorld", B = "fooBar"))), c("A", "B"))
+})
+
 # programming cases -----------------------------------------------------------
 
 test_that("to_camel can control case of first argument", {
diff --git a/tests/testthat/test-sub.R b/tests/testthat/test-sub.R
index d61ad2fe..945a9ad4 100644
--- a/tests/testthat/test-sub.R
+++ b/tests/testthat/test-sub.R
@@ -123,3 +123,9 @@ test_that("str_sub_all() preserves names on outer structure", {
   x <- c(C = "3", B = "2", A = "1")
   expect_equal(names(str_sub_all(x, 1, 1)), names(x))
 })
+
+test_that("str_sub<-() preserves names", {
+  x <- c(C = "3", B = "2", A = "1")
+  str_sub(x, 1, 1) <- c("X", "Y", "Z")
+  expect_equal(names(x), c("C", "B", "A"))
+})
diff --git a/tests/testthat/test-trim.R b/tests/testthat/test-trim.R
index a4b45972..61fb1f73 100644
--- a/tests/testthat/test-trim.R
+++ b/tests/testthat/test-trim.R
@@ -21,6 +21,36 @@ test_that("str_squish removes excess spaces from all parts of string", {
   expect_equal(str_squish("\ta\t bc\t"), "a bc")
 })
 
+test_that("str_trim handles NA values", {
+  expect_equal(str_trim(NA), NA_character_)
+  expect_equal(str_trim(c(NA, " abc ")), c(NA, "abc"))
+  expect_equal(str_trim(NA, "left"), NA_character_)
+  expect_equal(str_trim(NA, "right"), NA_character_)
+})
+
+test_that("str_squish handles NA values", {
+  expect_equal(str_squish(NA), NA_character_)
+  expect_equal(str_squish(c(NA, "  a  b  ")), c(NA, "a b"))
+})
+
+test_that("str_trim handles empty strings", {
+  expect_equal(str_trim(""), "")
+  expect_equal(str_trim("   "), "")
+})
+
+test_that("str_squish handles empty strings", {
+  expect_equal(str_squish(""), "")
+  expect_equal(str_squish("   "), "")
+})
+
+test_that("str_squish handles newlines and mixed whitespace", {
+  expect_equal(str_squish("a\n\nb"), "a b")
+  expect_equal(str_squish("\na\n"), "a")
+  expect_equal(str_squish("a\r\nb"), "a b")
+  expect_equal(str_squish("a\t\n b"), "a b")
+  expect_equal(str_squish("\t\n a \n\t b \t\n"), "a b")
+})
+
 test_that("trimming functions preserve names", {
   x <- c(C = "3", B = "2", A = "1")
   expect_equal(names(str_trim(x)), names(x))