diff --git a/NEWS.md b/NEWS.md
index 0828f7957f..c68d560725 100644
--- a/NEWS.md
+++ b/NEWS.md
@@ -5,6 +5,7 @@
   `NA`s (#5623)
 * Facet evaluation is better at dealing with inherited errors 
   (@teunbrand, #5670).
+* Fixed spurious warnings from `sec_axis()` with `breaks = NULL` (#5713).
 
 # ggplot2 3.5.0
 
diff --git a/R/axis-secondary.R b/R/axis-secondary.R
index 0c3fc4be6a..31ad994398 100644
--- a/R/axis-secondary.R
+++ b/R/axis-secondary.R
@@ -247,7 +247,7 @@ AxisSecondary <- ggproto("AxisSecondary", NULL,
       range_info <- temp_scale$break_info()
 
       # Map the break values back to their correct position on the primary scale
-      if (!is.null(range_info$major_source)) {
+      if (length(range_info$major_source) > 0) {
         old_val <- stats::approx(full_range, old_range, range_info$major_source)$y
         old_val_trans <- transformation$transform(old_val)
 
@@ -263,7 +263,7 @@ AxisSecondary <- ggproto("AxisSecondary", NULL,
         old_val_trans <- NULL
       }
 
-      if (!is.null(range_info$minor_source)) {
+      if (length(range_info$minor_source) > 0) {
         old_val_minor <- stats::approx(full_range, old_range, range_info$minor_source)$y
         old_val_minor_trans <- transformation$transform(old_val_minor)