diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3034fc0f..b2d6662b 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -89,9 +89,9 @@ set(SDRPP_MODULE_COMPILER_FLAGS ${SDRPP_COMPILER_FLAGS})
 # Set a default install prefix
 if (CMAKE_INSTALL_PREFIX_INITIALIZED_TO_DEFAULT)
     if (${CMAKE_SYSTEM_NAME} MATCHES "Darwin")
-        set(CMAKE_INSTALL_PREFIX "/usr/local")
+        set(CMAKE_INSTALL_PREFIX "/usr/local" CACHE PATH "..." FORCE)
     else()
-        set(CMAKE_INSTALL_PREFIX "/usr")
+        set(CMAKE_INSTALL_PREFIX "/usr" CACHE PATH "..." FORCE)
     endif()
 endif()