diff --git a/CMakeLists.txt b/CMakeLists.txt
index cf82dfdfc6..cbde769d3f 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -102,7 +102,7 @@ include("${CMAKE_BINARY_DIR}/vcpkg.cmake")
 if (HIFI_ANDROID)
   set(QT_CMAKE_PREFIX_PATH "$ENV{HIFI_ANDROID_PRECOMPILED}/qt/lib/cmake")
 else()
-  if (NOT $ENV{VIRCADIA_USE_SYSTEM_QT})
+  if (NOT DEFINED ENV{VIRCADIA_USE_SYSTEM_QT})
     if(NOT EXISTS "${CMAKE_BINARY_DIR}/qt.cmake")
         message(FATAL_ERROR "qt configuration missing.")
     endif()
@@ -293,7 +293,7 @@ set_packaging_parameters()
 # Locate the required Qt build on the filesystem
 setup_qt()
 
-if (NOT $ENV{VIRCADIA_USE_SYSTEM_QT})
+if (NOT DEFINED ENV{VIRCADIA_USE_SYSTEM_QT})
   list(APPEND CMAKE_PREFIX_PATH "${QT_CMAKE_PREFIX_PATH}")
 endif()
 
diff --git a/interface/CMakeLists.txt b/interface/CMakeLists.txt
index 9710aa53e8..267f996535 100644
--- a/interface/CMakeLists.txt
+++ b/interface/CMakeLists.txt
@@ -435,7 +435,7 @@ else()
   endif()
 endif()
 
-if (NOT $ENV{VIRCADIA_USE_SYSTEM_QT})
+if (NOT DEFINED ENV{VIRCADIA_USE_SYSTEM_QT})
   if (DEV_BUILD AND (APPLE OR UNIX))
     # create a qt.conf file to override hard-coded search paths in Qt libs
     set(QT_LIB_PATH "${QT_CMAKE_PREFIX_PATH}/../..")