diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 624a197299464f1cb2740697b04e289217ac636b..fa4c3725da9a54216aab1bde9eb4571e30ddfe28 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -46,7 +46,7 @@ stages:
         - export CTEST_OUTPUT_ON_FAILURE=1
         - export CTEST_PARALLEL_LEVEL=4
         # enforce (more or less) warning-free builds
-        - export CXXFLAGS="-Werror -Wno-error=deprecated -Wno-error=deprecated-declarations -Wno-error=uninitialized -Wno-error=vla"
+        #- export CXXFLAGS="-Werror -Wno-error=deprecated -Wno-error=deprecated-declarations -Wno-error=uninitialized -Wno-error=vla"
         - mkdir -p "./builddir/$CI_JOB_NAME"
         - pushd "./builddir/$CI_JOB_NAME"
         - cmake ../..
@@ -64,6 +64,7 @@ stages:
                 -DWITH_EXAMPLES=${WITH_EXAMPLES}
                 -DWITH_TOOLS=${WITH_TOOLS}
                 -DWITH_PYTHON=${WITH_PYTHON}
+                -DWITH_CI_FLAGS=yes
         # "install" implies the "all" target
         - ninja ${NINJAFLAGS} install
         - if [[ ${WITH_TESTS} == "yes" ]]; then
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7d1666163bb19c786d9104cbcd9d81731844931b..a312b00cb92e3026513c1090b57c724c8907bc13 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -96,6 +96,11 @@ set( CMAKE_SHARED_LINKER_FLAGS "" )
 set( CMAKE_SHARED_LINKER_FLAGS_DEBUG "-rdynamic" )
 set( CMAKE_SHARED_LINKER_FLAGS_RELEASE "" )
 
+if( ${WITH_CI_FLAGS} )
+   # enforce (more or less) warning-free builds
+   set( CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations -Wno-error=uninitialized -Wno-error=vla" )
+endif()
+
 # set additional Debug/Release options using generator expressions
 # (that way we can exclude some options for specific targets, see https://stackoverflow.com/a/59734798 for details)
 add_compile_options(
diff --git a/build b/build
index 9deb12d10a19ec272ed54ee7512580ed7bd4d71b..5a26cbb6193beafa66a5a64063476cb6a0faa6bc 100755
--- a/build
+++ b/build
@@ -31,6 +31,7 @@ WITH_EXAMPLES="yes"
 WITH_PYTHON="yes"
 WITH_TOOLS="yes"
 WITH_BENCHMARKS="yes"
+WITH_CI_FLAGS="no"
 
 for option in "$@"
 do
@@ -63,6 +64,7 @@ do
         --with-benchmarks=*              ) WITH_BENCHMARKS="${option#*=}" ;;
         --with-python=*                  ) WITH_PYTHON="${option#*=}" ;;
         --with-cxx-flags=*               ) WITH_CXX_FLAGS="${option#*=}" ;;
+        --with-ci-flags=*                ) WITH_CI_FLAGS="${option#*=}" ;;
         *                                )
            echo "Unknown option ${option}. Use --help for more information."
            exit 1 ;;
@@ -93,6 +95,7 @@ if [[ ${HELP} == "yes" ]]; then
     echo "   --with-python=yes/no                  Compile the Python bindings. 'yes' by default."
     echo "   --with-benchmarks=yes/no              Compile the 'src/Benchmarks' directory. 'yes' by default."
     echo "   --with-cxx-flags=FLAGS                Additional flags for C++ compiler."
+    echo "   --with-cxx-flags=yes/no               Turns on more strict C++ flags for CI. 'no' by default."
     echo "   --cmake=CMAKE                         Path to cmake. 'cmake' by default."
     echo "   --verbose                             It enables verbose build."
     echo "   --root-dir=PATH                       Path to the TNL source code root dir."
@@ -145,6 +148,7 @@ cmake_command=(
          -DWITH_PYTHON=${WITH_PYTHON}
          -DWITH_BENCHMARKS=${WITH_BENCHMARKS}
          -DWITH_CXX_FLAGS=${WITH_CXX_FLAGS}
+         -DWITH_CI_FLAGS=${WITH_CI_FLAGS}
          -DDCMTK_DIR=${DCMTK_DIR}
 )