diff --git a/cmake/modules/BuildBoost.cmake b/cmake/modules/BuildBoost.cmake
index d6572115a4..cc0bdddc9f 100644
--- a/cmake/modules/BuildBoost.cmake
+++ b/cmake/modules/BuildBoost.cmake
@@ -62,7 +62,7 @@ function(do_build_boost version)
   else()
     list(APPEND boost_features "address-model=32")
   endif()
-  set(BOOST_CXXFLAGS "-fPIC -w") # check on arm, etc <---XXX
+  set(BOOST_CXXFLAGS "${CMAKE_CXX_FLAGS} -fPIC -w") # check on arm, etc <---XXX
   list(APPEND boost_features "cxxflags=${BOOST_CXXFLAGS}")
 
   list(FIND Boost_BUILD_COMPONENTS "python" with_python)
diff --git a/src/compressor/zstd/CMakeLists.txt b/src/compressor/zstd/CMakeLists.txt
index 5a80aa539c..8d6ff5c8f0 100644
--- a/src/compressor/zstd/CMakeLists.txt
+++ b/src/compressor/zstd/CMakeLists.txt
@@ -1,7 +1,7 @@
 # zstd
 
 # libzstd - build it statically
-set(ZSTD_C_FLAGS "-fPIC -Wno-unused-variable -O3")
+set(ZSTD_C_FLAGS "-fPIC -Wno-unused-variable $ENV{CFLAGS} -O3")
 
 include(ExternalProject)
 ExternalProject_Add(zstd_ext