diff --git a/src/app/components/AvailableModulesMenu.jsx b/src/app/components/AvailableModulesMenu.jsx
index 94cd0e23..d1a71bda 100644
--- a/src/app/components/AvailableModulesMenu.jsx
+++ b/src/app/components/AvailableModulesMenu.jsx
@@ -286,6 +286,8 @@ export default class AvailableModulesMenu extends TranslatedComponent {
       // the maximum does not apply
       } else if (m.experimental && (!mountedModule || !mountedModule.experimental)) {
         disabled = 4 <= ship.hardpoints.filter(o => o.m && o.m.experimental).length;
+      } else if (m.grp === 'mlc' && mountedModule.grp !== 'mlc') {
+        disabled = 1 <= ship.internal.filter(o => o.m && o.m.grp === 'mlc').length;
       }
       let active = mountedModule && mountedModule.id === m.id;
       let classes = cn(m.name ? 'lc' : 'c', {