diff --git a/R/data_modify.R b/R/data_modify.R
index f1d6fa5c6..7dbcc5319 100644
--- a/R/data_modify.R
+++ b/R/data_modify.R
@@ -352,22 +352,16 @@ data_modify.grouped_df <- function(data, ..., .if = NULL, .at = NULL, .modify =
       .misspelled_string(column_names, not_found, "Possibly misspelled or not yet defined?")
     )
   }
-  # modify variables
-  found <- .at[.at %in% column_names]
-  if (length(found)) {
-    for (i in found) {
-      result <- tryCatch(.modify(data[[i]]), warning = function(e) e, error = function(e) e)
-      if (inherits(result, c("error", "warning"))) {
-        insight::format_error(
-          paste0("Error in modifying variable \"", i, "\": ", result$message),
-          "Please check if you correctly specified the `.modify` function."
-        )
-      } else {
-        data[[i]] <- result
-      }
+  for (i in .at) {
+    result <- tryCatch(.modify(data[[i]]), warning = function(e) e, error = function(e) e)
+    if (inherits(result, c("error", "warning"))) {
+      insight::format_error(
+        paste0("Error in modifying variable \"", i, "\": ", result$message),
+        "Please check if you correctly specified the `.modify` function."
+      )
+    } else {
+      data[[i]] <- result
     }
-  } else {
-    insight::format_error("No variables found in the dataset that match the `.if` or `.at` argument.")
   }
 
   data
diff --git a/tests/testthat/test-data_modify.R b/tests/testthat/test-data_modify.R
index dac902d66..66453b6c0 100644
--- a/tests/testthat/test-data_modify.R
+++ b/tests/testthat/test-data_modify.R
@@ -513,24 +513,23 @@ test_that("data_modify .if/.at arguments", {
     data_modify(d, .at = "Species", .modify = "a"),
     regex = "`.modify` must"
   )
-  expect_message(
+  expect_error(
     data_modify(d, .at = c("Species", "Test"), .modify = as.numeric),
     regex = "Variable \"Test\""
   )
-  expect_message(
+  expect_error(
     data_modify(d, .at = c("Species", "Hi", "Test"), .modify = as.numeric),
     regex = "Variables \"Hi\" and \"Test\""
   )
-  expect_message(
-    data_modify(d, .at = c("Hi", "Test"), .modify = as.numeric),
-    regex = "No variables found in the dataset"
-  )
   expect_error(
     data_modify(d, .at = "Species", .modify = function(x) 2 / y + x),
     regex = "Error in modifying variable"
   )
-  expect_warning(
+  expect_error(
     data_modify(d, .at = "Species", .modify = function(x) 2 * x),
-    regex = "Warning when modifying variable"
+    regex = "Error in modifying variable"
   )
+  # newly created variables are not modified by if/at
+  out <- data_modify(d, new_length = Petal.Length * 2, .if = is.numeric, .modify = as.factor)
+  expect_identical(out$new_length, c(2.8, 2.8, 2.6, 3, 2.8))
 })