diff --git a/CMakeLists.txt b/CMakeLists.txt
index 477158a7..b2135c3e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1008,7 +1008,8 @@ if (COOLPROP_MATLAB_SWIG_MODULE)
   endif()
   
   add_dependencies (CoolPropMATLAB_wrap generate_headers)
-  if (not COOLPROP_MATLAB_INSTALL_PREFIX)
+  if (COOLPROP_MATLAB_INSTALL_PREFIX)
+  else()
     set(COOLPROP_MATLAB_INSTALL_PREFIX ${COOLPROP_INSTALL_PREFIX}/MATLAB)
   endif()
   install (FILES ${CMAKE_CURRENT_BINARY_DIR}/+CoolProp.7z DESTINATION ${COOLPROP_MATLAB_INSTALL_PREFIX})