diff --git a/backend/src/utils/validation.ts b/backend/src/utils/validation.ts
index a36ea508c..e5ef947e4 100644
--- a/backend/src/utils/validation.ts
+++ b/backend/src/utils/validation.ts
@@ -136,6 +136,10 @@ export function areFunboxesCompatible(funboxesString: string): boolean {
   const oneCharReplacerMax =
     funboxesToCheck.filter((f) => f.frontendFunctions?.includes("getWordHtml"))
       .length <= 1;
+  const oneChangesCapitalisationMax =
+    funboxesToCheck.filter((f) =>
+      f.properties?.find((fp) => fp === "changesCapitalisation")
+    ).length <= 1;
   const allowedConfig = {} as Record<string, string[] | boolean[]>;
   let noConfigConflicts = true;
   for (const f of funboxesToCheck) {
@@ -174,6 +178,7 @@ export function areFunboxesCompatible(funboxesString: string): boolean {
     onePunctuateWordMax &&
     oneCharCheckerMax &&
     oneCharReplacerMax &&
+    oneChangesCapitalisationMax &&
     noConfigConflicts &&
     oneWordOrderMax
   );
diff --git a/frontend/src/ts/test/funbox/funbox-validation.ts b/frontend/src/ts/test/funbox/funbox-validation.ts
index 31b132b9d..0f0bf1cfd 100644
--- a/frontend/src/ts/test/funbox/funbox-validation.ts
+++ b/frontend/src/ts/test/funbox/funbox-validation.ts
@@ -296,6 +296,10 @@ export function areFunboxesCompatible(
     funboxesToCheck.filter((f) => f.functions?.isCharCorrect).length <= 1;
   const oneCharReplacerMax =
     funboxesToCheck.filter((f) => f.functions?.getWordHtml).length <= 1;
+  const oneChangesCapitalisationMax =
+    funboxesToCheck.filter((f) =>
+      f.properties?.find((fp) => fp === "changesCapitalisation")
+    ).length <= 1;
   const allowedConfig = {} as FunboxForcedConfig;
   let noConfigConflicts = true;
   for (const f of funboxesToCheck) {
@@ -335,6 +339,7 @@ export function areFunboxesCompatible(
     onePunctuateWordMax &&
     oneCharCheckerMax &&
     oneCharReplacerMax &&
+    oneChangesCapitalisationMax &&
     noConfigConflicts
   );
 }