diff --git a/gtsam/CMakeLists.txt b/gtsam/CMakeLists.txt
index bceca6bcd..859f61513 100644
--- a/gtsam/CMakeLists.txt
+++ b/gtsam/CMakeLists.txt
@@ -137,7 +137,7 @@ endif()
 
 # make sure that ccolamd compiles even in face of warnings
 if(WIN32)
-    set_source_files_properties(${3rdparty_srcs} PROPERTIES COMPILE_FLAGS "/w")
+    set_source_files_properties(${3rdparty_srcs} PROPERTIES COMPILE_FLAGS "-w")
 else()
     set_source_files_properties(${3rdparty_srcs} PROPERTIES COMPILE_FLAGS "-Wno-error")
 endif()