diff --git a/dll/win32/rpcrt4/CMakeLists.txt b/dll/win32/rpcrt4/CMakeLists.txt
index 212231a3a24..24c5d8fb406 100644
--- a/dll/win32/rpcrt4/CMakeLists.txt
+++ b/dll/win32/rpcrt4/CMakeLists.txt
@@ -14,9 +14,10 @@ spec2def(rpcrt4.dll rpcrt4.spec ADD_IMPORTLIB)
 add_rpc_files(client epm.idl)
 add_idl_headers(ndr_types_header ndr_types.idl)
 
+set(OLD_IDL_FLAGS ${IDL_FLAGS})
 set(IDL_FLAGS ${IDL_FLAGS} -Oicf)
 add_rpcproxy_files(ndr_types.idl)
-unset(IDL_FLAGS)
+set(IDL_FLAGS ${OLD_IDL_FLAGS})
 
 list(APPEND SOURCE
     cproxy.c
diff --git a/modules/rostests/winetests/rpcrt4/CMakeLists.txt b/modules/rostests/winetests/rpcrt4/CMakeLists.txt
index dbb7cf7fc11..4eeac9d3af2 100644
--- a/modules/rostests/winetests/rpcrt4/CMakeLists.txt
+++ b/modules/rostests/winetests/rpcrt4/CMakeLists.txt
@@ -7,10 +7,11 @@ add_definitions(
     -DPROXY_DELEGATION)
 
 include_directories(${CMAKE_CURRENT_BINARY_DIR})
+set(OLD_IDL_FLAGS ${IDL_FLAGS})
 set(IDL_FLAGS ${IDL_FLAGS} --prefix-server=s_)
 add_rpc_files(client server.idl)
 add_rpc_files(server server.idl)
-unset(IDL_FLAGS)
+set(IDL_FLAGS ${OLD_IDL_FLAGS})
 add_rpcproxy_files(cstub.idl)
 
 list(APPEND SOURCE