diff --git a/cmake/cpp.cmake b/cmake/cpp.cmake
index 78e6fa82e85..c867adad006 100644
--- a/cmake/cpp.cmake
+++ b/cmake/cpp.cmake
@@ -203,7 +203,7 @@ if(USE_PDLP)
   file(GLOB_RECURSE pdlp_proto_files RELATIVE ${PROJECT_SOURCE_DIR} "ortools/pdlp/*.proto")
   list(APPEND proto_files ${pdlp_proto_files})
 endif()
-if(USE_SCIP)
+if(USE_SCIP OR BUILD_MATH_OPT)
   file(GLOB_RECURSE gscip_proto_files RELATIVE ${PROJECT_SOURCE_DIR} "ortools/gscip/*.proto")
   list(APPEND proto_files ${gscip_proto_files})
 endif()