diff --git a/NEWS.md b/NEWS.md
index 335ced6..286a38f 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -3,6 +3,7 @@
 * Fixed an issue where disabling line statement could raise an error during template parsing. Since line statements are disabled by default, this error could be encountered quite easily (#31).
 * `quote_sql()` now escapes single-quotes using an additional single-quote (#30).
 * Fixed edge case in how error messages are formatted (#32).
+* `render()` now validates data variables are supported (#25).
 
 
 # jinjar 0.3.0
diff --git a/R/encode.R b/R/encode.R
index 8503066..465fc73 100644
--- a/R/encode.R
+++ b/R/encode.R
@@ -11,6 +11,18 @@ encode <- function(...) {
     ))
   }
 
+  for (name in names(data)) {
+    x <- data[[name]]
+    if (!(is_null(x) || is_logical(x) || is_integer(x) || is_double(x) || is_character(x)
+          || is_bare_list(x) || inherits_any(x, "data.frame"))) {
+      cli::cli_abort(c(
+        "Data variable {.arg {name}} is unsupported.",
+        "x" = "{.arg {name}} is {.obj_type_friendly {x}}.",
+        "i" = "Choices: NULL, logical, integer, double, character, list, dataframe."
+      ))
+    }
+  }
+
   jsonlite::toJSON(
     data,
     auto_unbox = TRUE, # length-1 vectors output as scalars
diff --git a/tests/testthat/_snaps/encode.md b/tests/testthat/_snaps/encode.md
index e5d95a7..d34c729 100644
--- a/tests/testthat/_snaps/encode.md
+++ b/tests/testthat/_snaps/encode.md
@@ -16,3 +16,13 @@
       ! All data variables must be named.
       x Unnamed variables: `b` and `mtcars`
 
+# data validation works
+
+    Code
+      encode(a = mean)
+    Condition
+      Error in `encode()`:
+      ! Data variable `a` is unsupported.
+      x `a` is a function.
+      i Choices: NULL, logical, integer, double, character, list, dataframe.
+
diff --git a/tests/testthat/test-encode.R b/tests/testthat/test-encode.R
index a790732..0a14f16 100644
--- a/tests/testthat/test-encode.R
+++ b/tests/testthat/test-encode.R
@@ -6,3 +6,7 @@ test_that("dynamic dots work", {
   expect_equal(encode(a = 1), res)
   expect_equal(encode(!!!list(a = 1)), res)
 })
+
+test_that("data validation works", {
+  expect_snapshot(encode(a = mean), error = TRUE)
+})