diff --git a/change/@fluentui-react-calendar-compat-8241b3ac-9f23-473b-be97-cfbe2c70475d.json b/change/@fluentui-react-calendar-compat-8241b3ac-9f23-473b-be97-cfbe2c70475d.json
new file mode 100644
index 0000000000000..ad6e8d66725e0
--- /dev/null
+++ b/change/@fluentui-react-calendar-compat-8241b3ac-9f23-473b-be97-cfbe2c70475d.json
@@ -0,0 +1,7 @@
+{
+  "type": "patch",
+  "comment": "fix: Classnames removed and added to day cells need to be split instead of providing a string with spaces.",
+  "packageName": "@fluentui/react-calendar-compat",
+  "email": "esteban.230@hotmail.com",
+  "dependentChangeType": "patch"
+}
diff --git a/packages/react-components/react-calendar-compat/src/components/CalendarDayGrid/CalendarGridDayCell.tsx b/packages/react-components/react-calendar-compat/src/components/CalendarDayGrid/CalendarGridDayCell.tsx
index 843d53be01a8e..2d4aaca5114ca 100644
--- a/packages/react-components/react-calendar-compat/src/components/CalendarDayGrid/CalendarGridDayCell.tsx
+++ b/packages/react-components/react-calendar-compat/src/components/CalendarDayGrid/CalendarGridDayCell.tsx
@@ -137,7 +137,7 @@ export const CalendarGridDayCell: React.FunctionComponent<CalendarGridDayCellPro
 
           const classNamesToAdd = calculateRoundedStyles(false, false, index > 0, index < dayRefs.length - 1).trim();
           if (classNamesToAdd) {
-            dayRef.classList.add(...classNamesToAdd);
+            dayRef.classList.add(...classNamesToAdd.trim().split(' '));
           }
         }
       }
@@ -182,7 +182,7 @@ export const CalendarGridDayCell: React.FunctionComponent<CalendarGridDayCellPro
         ) {
           const classNamesToAdd = calculateRoundedStyles(false, false, index > 0, index < dayRefs.length - 1).trim();
           if (classNamesToAdd) {
-            dayRef.classList.remove(...classNamesToAdd);
+            dayRef.classList.remove(...classNamesToAdd.trim().split(' '));
           }
         }
       }