diff --git a/NEWS.md b/NEWS.md
index c69ea43fbc..ebc4be39e9 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -24,6 +24,9 @@
   legend glyphs (@teunbrand, #6594)
 * Fixed regression where `NULL`-aesthetics contributed to plot labels too 
   insistently. Now they contribute only as fallback labels (@teunbrand, #6616)
+* The `theme(panel.widths, panel.heights)` setting attempts to preserve the
+  plot's aspect ratio when only one of the two settings is given, and the plot 
+  has a single panel (@teunbrand, #6701).
 * Fixed axis misplacement in `coor_radial()` when labels are blank (@teunbrand, #6574)
 
 # ggplot2 4.0.0
diff --git a/R/facet-.R b/R/facet-.R
index e4a010d612..7aa06695d0 100644
--- a/R/facet-.R
+++ b/R/facet-.R
@@ -731,18 +731,24 @@ Facet <- ggproto("Facet", NULL,
       return(table)
     }
 
-    if (isTRUE(table$respect)) {
-      args <- !c(is.null(new_widths), is.null(new_heights))
-      args <- c("panel.widths", "panel.heights")[args]
-      cli::cli_warn(
-        "Aspect ratios are overruled by {.arg {args}} theme element{?s}."
-      )
-      table$respect <- FALSE
-    }
-
     rows <- panel_rows(table)
     cols <- panel_cols(table)
 
+    if (isTRUE(table$respect) && # Has fixed aspect ratio
+        xor(is.null(new_widths), is.null(new_heights)) && # One dimension is set
+        nrow(rows) == 1 && nrow(cols) == 1) { # Just a single panel
+      old_width <- table$widths[cols$l]
+      old_height <- table$heights[rows$t]
+      # Try to reconstruct aspect ratio from panel size
+      # We shouldn't attempt this with mixed or compound (e.g. "sum") units
+      if (identical(unitType(old_width),  "null") &&
+          identical(unitType(old_height), "null")) {
+        ratio <- as.numeric(old_height) / as.numeric(old_width)
+        new_widths  <- (new_widths  %||% (new_heights / ratio))[1]
+        new_heights <- (new_heights %||% (new_widths  * ratio))[1]
+      }
+    }
+
     if (length(new_widths) == 1L && nrow(cols) > 1L) {
       # Get total size of non-panel widths in between panels
       extra <- setdiff(seq(min(cols$l), max(cols$r)), union(cols$l, cols$r))
diff --git a/R/theme.R b/R/theme.R
index 07a13db64a..bab9e23b5a 100644
--- a/R/theme.R
+++ b/R/theme.R
@@ -151,7 +151,10 @@
 #'   from `line`
 #' @param panel.widths,panel.heights Sizes for panels (`units`). Can be a
 #'   single unit to set the total size for the panel area, or a unit vector to
-#'   set the size of individual panels.
+#'   set the size of individual panels. Using this setting overrides the
+#'   aspect ratio set by the theme, coord or facets. An exception is made when
+#'   the plot has a single panel and exactly one of the width *or* height is
+#'   set, in which case an attempt is made to preserve the aspect ratio.
 #' @param panel.ontop option to place the panel (background, gridlines) over
 #'   the data layers (`logical`). Usually used with a transparent or blank
 #'   `panel.background`.
diff --git a/man/theme.Rd b/man/theme.Rd
index ad95fb1d86..66a9be0d32 100644
--- a/man/theme.Rd
+++ b/man/theme.Rd
@@ -327,7 +327,10 @@ the data layers (\code{logical}). Usually used with a transparent or blank
 
 \item{panel.widths, panel.heights}{Sizes for panels (\code{units}). Can be a
 single unit to set the total size for the panel area, or a unit vector to
-set the size of individual panels.}
+set the size of individual panels. Using this setting overrides the
+aspect ratio set by the theme, coord or facets. An exception is made when
+the plot has a single panel and exactly one of the width \emph{or} height is
+set, in which case an attempt is made to preserve the aspect ratio.}
 
 \item{plot.background}{background of the entire plot (\code{\link[=element_rect]{element_rect()}};
 inherits from \code{rect})}
diff --git a/tests/testthat/test-theme.R b/tests/testthat/test-theme.R
index 3f3fb9eeb9..d8508f9070 100644
--- a/tests/testthat/test-theme.R
+++ b/tests/testthat/test-theme.R
@@ -717,11 +717,34 @@ test_that("panel.widths and panel.heights works with free-space panels", {
 
 })
 
-test_that("panel.widths and panel.heights appropriately warn about aspect override", {
-  p <- ggplot(mpg, aes(displ, hwy)) +
-    geom_point() +
-    theme(aspect.ratio = 1, panel.widths = unit(4, "cm"))
-  expect_warning(ggplotGrob(p), "Aspect ratios are overruled")
+test_that("panel.withs and panel.heights preserve aspect ratios with single panels", {
+
+  df <- data.frame(x = c(1, 2))
+
+  p <- ggplotGrob(
+    ggplot(df, aes(x, x)) +
+      geom_point() +
+      theme(
+        aspect.ratio = 2,
+        panel.heights = unit(10, "cm")
+      )
+  )
+
+  width <- p$widths[panel_cols(p)$l]
+  expect_equal(as.character(width), "5cm")
+
+  p <- ggplotGrob(
+    ggplot(df, aes(x, x)) +
+      geom_point() +
+      facet_wrap(~ x) + # This behaviour doesn't occur in multipanel plots.
+      theme(
+        aspect.ratio = 2,
+        panel.heights = unit(10, "cm")
+      )
+  )
+
+  width <- p$widths[panel_cols(p)$l]
+  expect_equal(as.character(width), c("1null", "1null"))
 })
 
 test_that("margin_part() mechanics work as expected", {