diff --git a/NEWS.md b/NEWS.md
index d1a85c4e4..cc99bd575 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -11,6 +11,12 @@
 
 - Fixes for CRAN check failures (#1645)
 
+- Avoid overwriting Altair's default chart dimensions
+  with the values of `ut.width.px` and `ut.height.px`.
+  Instead, use `altair.fig.height`, `altair.fig.width`,
+  or Altair's `width` and `height` parameters
+  to adjust chart dimensions.
+
 - New `as.raw()` method for `python.builtin.bytes` (#1649, #1652)
 
 - `as.character()` method for `python.builtin.bytes` gains a `nul` argument,
diff --git a/R/knitr-engine.R b/R/knitr-engine.R
index 0876b59fe..dd2e3fbe4 100644
--- a/R/knitr-engine.R
+++ b/R/knitr-engine.R
@@ -767,22 +767,18 @@ eng_python_autoprint <- function(captured, options) {
 
   } else if (eng_python_is_altair_chart(value)) {
 
-    # set width if it's not already set
+    # set width and height if it's not already set
     # This only applies to Chart objects, compound charts like HConcatChart
     # don't have a 'width' or 'height' property attribute.
     # TODO: add support for propagating width/height options from knitr to
     # altair compound charts
     width <- py_get_attr(value, "width", TRUE)
-    if (inherits(width, "altair.utils.schemapi.UndefinedType")) {
-      width <- options$altair.fig.width %||% options$out.width.px %||% 810L
-      value <- value$properties(width = width)
+    if (!is.null(options$altair.fig.width)) {
+      value <- value$properties(width = options$altair.fig.width)
     }
-
-    # set height if it's not already set
     height <- py_get_attr(value, "height", TRUE)
-    if (inherits(height, "altair.utils.schemapi.UndefinedType")) {
-      height <- options$altair.fig.height %||% options$out.height.px %||% 400L
-      value <- value$properties(height = height)
+    if (!is.null(options$altair.fig.height)) {
+      value <- value$properties(height = options$altair.fig.height)
     }
 
     # set a unique id (used for div container for figure)