diff --git a/CHANGELOG.md b/CHANGELOG.md
index 746e37e..69195c2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,9 @@ All notable changes to eww will be listed here, starting at changes since versio
 
 ## [Unreleased]
 
+### BREAKING CHANGES
+- Change `calendar`-widget to index months starting at 1 rather than indexed from 0
+
 ### Features
 - Add support for output names in X11 to select `:monitor`.
 
diff --git a/crates/eww/src/widgets/widget_definitions.rs b/crates/eww/src/widgets/widget_definitions.rs
index fd7532f..3ec63cd 100644
--- a/crates/eww/src/widgets/widget_definitions.rs
+++ b/crates/eww/src/widgets/widget_definitions.rs
@@ -904,9 +904,21 @@ fn build_gtk_calendar(bargs: &mut BuilderArgs) -> Result<gtk::Calendar> {
     let gtk_widget = gtk::Calendar::new();
     def_widget!(bargs, _g, gtk_widget, {
         // @prop day - the selected day
-        prop(day: as_f64) { gtk_widget.set_day(day as i32) },
+        prop(day: as_f64) {
+            if day < 1f64 || day > 31f64 {
+                log::warn!("Calendar day is not a number between 1 and 31");
+            } else {
+                gtk_widget.set_day(day as i32)
+            }
+        },
         // @prop month - the selected month
-        prop(month: as_f64) { gtk_widget.set_month(month as i32) },
+        prop(month: as_f64) {
+            if month < 1f64 || month > 12f64 {
+                log::warn!("Calendar month is not a number between 1 and 12");
+            } else {
+                gtk_widget.set_month(month as i32 - 1)
+            }
+        },
         // @prop year - the selected year
         prop(year: as_f64) { gtk_widget.set_year(year as i32) },
         // @prop show-details - show details