diff --git a/xs/CMakeLists.txt b/xs/CMakeLists.txt
index efd52ac137..d19aad70a3 100644
--- a/xs/CMakeLists.txt
+++ b/xs/CMakeLists.txt
@@ -503,7 +503,7 @@ if (WIN32)
 endif ()
 
 # SLIC3R_MSVC_PDB
-if (MSVC AND SLIC3R_MSVC_PDB AND ${CMAKE_BUILD_TYPE} STREQUAL "Release")
+if (MSVC AND SLIC3R_MSVC_PDB AND "${CMAKE_BUILD_TYPE}" STREQUAL "Release")
     set_target_properties(XS PROPERTIES
         COMPILE_FLAGS "/Zi"
         LINK_FLAGS "/DEBUG /OPT:REF /OPT:ICF"