diff --git a/css/backoffice/components/_fieldset.scss b/css/backoffice/components/_fieldset.scss
index e03008b9a..eb0b71e1d 100644
--- a/css/backoffice/components/_fieldset.scss
+++ b/css/backoffice/components/_fieldset.scss
@@ -17,6 +17,7 @@ $ibo-fieldset--legend--border-bottom-style: solid !default;
     margin-top: $ibo-fieldset--sibling-spacing;
   }
 }
+
 .ibo-fieldset-legend {
   width: $ibo-fieldset--legend--width;
   margin-bottom: $ibo-fieldset--legend--margin-bottom;
@@ -25,3 +26,19 @@ $ibo-fieldset--legend--border-bottom-style: solid !default;
 
   @extend %ibo-font-ral-med-250;
 }
+
+/* For compatibility with extensions before 3.0.0 */
+fieldset {
+  &:not(.ibo-fieldset) {
+    margin: 10px;
+
+    & legend {
+      width: $ibo-fieldset--legend--width;
+      margin-bottom: $ibo-fieldset--legend--margin-bottom;
+      padding-bottom: $ibo-fieldset--legend--padding-bottom;
+      border-bottom: $ibo-fieldset--legend--border-bottom-size $ibo-fieldset--legend--border-bottom-style $ibo-fieldset--legend--border-bottom-color;
+
+      @extend %ibo-font-ral-med-250;
+    }
+  }
+}
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