diff --git a/lib/CMakeLists.txt b/lib/CMakeLists.txt
index 8a4bd71..1927fb0 100644
--- a/lib/CMakeLists.txt
+++ b/lib/CMakeLists.txt
@@ -111,7 +111,7 @@ if(CMAKE_SYSTEM_NAME STREQUAL "WindowsStore")
   add_definitions(-D_WINSOCK_DEPRECATED_NO_WARNINGS)
 endif()
 
-if(WIN32)
+if(WIN32 AND BUILD_SHARED_LIBS)
   add_definitions(-D_USRDLL)
 endif()