diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7e481c17d..a47a2ffbf 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -250,7 +250,7 @@ if (MSVC)
       -machine:X64)
 else ()
   # HACK : because these need to come first, before any warning demotion
-  string (APPEND CMAKE_CXX_FLAGS "-Wall -Wdeprecated")
+  string (APPEND CMAKE_CXX_FLAGS " -Wall -Wdeprecated")
   # not MSVC
   target_compile_options (common
     INTERFACE