diff --git src/group_gui.cpp src/group_gui.cpp
index 06f56b9..b7e8ab1 100644
--- src/group_gui.cpp
+++ src/group_gui.cpp
@@ -669,7 +669,7 @@ public:
 			case WID_GL_REPLACE_PROTECTION: {
 				const Group *g = Group::GetIfValid(this->vli.index);
 				if (g != NULL) {
-					DoCommandP(0, this->vli.index, !g->replace_protection | (_ctrl_pressed << 1), CMD_SET_GROUP_REPLACE_PROTECTION);
+					DoCommandP(0, this->vli.index, (!g->replace_protection) | (_ctrl_pressed << 1), CMD_SET_GROUP_REPLACE_PROTECTION);
 				}
 				break;
 			}