diff --git a/cmake/ci.cmake b/cmake/ci.cmake
index 4e7e4dcc2..eef7345b4 100644
--- a/cmake/ci.cmake
+++ b/cmake/ci.cmake
@@ -416,7 +416,7 @@ set(GCC_CXXFLAGS
 add_custom_target(ci_test_gcc
     COMMAND CXX=${GCC_TOOL} CXXFLAGS="${GCC_CXXFLAGS}" ${CMAKE_COMMAND}
         -DCMAKE_BUILD_TYPE=Debug -GNinja
-        -DJSON_BuildTests=ON
+        -DJSON_BuildTests=ON -DJSON_32bitTest=AUTO
         -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_gcc
     COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_gcc
     COMMAND cd ${PROJECT_BINARY_DIR}/build_gcc && ${CMAKE_CTEST_COMMAND} --parallel ${N} --output-on-failure
@@ -426,7 +426,7 @@ add_custom_target(ci_test_gcc
 add_custom_target(ci_test_clang
     COMMAND CXX=${CLANG_TOOL} CXXFLAGS="${CLANG_CXXFLAGS}" ${CMAKE_COMMAND}
         -DCMAKE_BUILD_TYPE=Debug -GNinja
-        -DJSON_BuildTests=ON -DJSON_32bitTest=ON
+        -DJSON_BuildTests=ON -DJSON_32bitTest=AUTO
         -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_clang
     COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_clang
     COMMAND cd ${PROJECT_BINARY_DIR}/build_clang && ${CMAKE_CTEST_COMMAND} --parallel ${N} --output-on-failure
@@ -441,7 +441,7 @@ foreach(CXX_STANDARD 11 14 17 20)
     add_custom_target(ci_test_gcc_cxx${CXX_STANDARD}
         COMMAND CXX=${GCC_TOOL} CXXFLAGS="${GCC_CXXFLAGS}" ${CMAKE_COMMAND}
             -DCMAKE_BUILD_TYPE=Debug -GNinja
-            -DJSON_BuildTests=ON -DJSON_FastTests=ON
+            -DJSON_BuildTests=ON -DJSON_FastTests=ON -DJSON_32bitTest=AUTO
             -DJSON_TestStandards=${CXX_STANDARD}
             -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_gcc_cxx${CXX_STANDARD}
         COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_gcc_cxx${CXX_STANDARD}
@@ -452,7 +452,7 @@ foreach(CXX_STANDARD 11 14 17 20)
     add_custom_target(ci_test_clang_cxx${CXX_STANDARD}
         COMMAND CXX=${CLANG_TOOL} CXXFLAGS="${CLANG_CXXFLAGS}" ${CMAKE_COMMAND}
             -DCMAKE_BUILD_TYPE=Debug -GNinja
-            -DJSON_BuildTests=ON -DJSON_FastTests=ON -DJSON_32bitTest=ON
+            -DJSON_BuildTests=ON -DJSON_FastTests=ON -DJSON_32bitTest=AUTO
             -DJSON_TestStandards=${CXX_STANDARD}
             -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_clang_cxx${CXX_STANDARD}
         COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_clang_cxx${CXX_STANDARD}
@@ -468,7 +468,7 @@ endforeach()
 add_custom_target(ci_test_noexceptions
     COMMAND CXX=${CLANG_TOOL} ${CMAKE_COMMAND}
     -DCMAKE_BUILD_TYPE=Debug -GNinja
-    -DJSON_BuildTests=ON -DJSON_32bitTest=ON -DCMAKE_CXX_FLAGS=-DJSON_NOEXCEPTION -DDOCTEST_TEST_FILTER=--no-throw
+    -DJSON_BuildTests=ON -DJSON_32bitTest=AUTO -DCMAKE_CXX_FLAGS=-DJSON_NOEXCEPTION -DDOCTEST_TEST_FILTER=--no-throw
     -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_noexceptions
     COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_noexceptions
     COMMAND cd ${PROJECT_BINARY_DIR}/build_noexceptions && ${CMAKE_CTEST_COMMAND} --parallel ${N} --output-on-failure
@@ -482,7 +482,7 @@ add_custom_target(ci_test_noexceptions
 add_custom_target(ci_test_noimplicitconversions
     COMMAND CXX=${CLANG_TOOL} ${CMAKE_COMMAND}
     -DCMAKE_BUILD_TYPE=Debug -GNinja
-    -DJSON_BuildTests=ON -DJSON_ImplicitConversions=OFF -DJSON_32bitTest=ON
+    -DJSON_BuildTests=ON -DJSON_ImplicitConversions=OFF -DJSON_32bitTest=AUTO
     -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_noimplicitconversions
     COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_noimplicitconversions
     COMMAND cd ${PROJECT_BINARY_DIR}/build_noimplicitconversions && ${CMAKE_CTEST_COMMAND} --parallel ${N} --output-on-failure
@@ -496,7 +496,7 @@ add_custom_target(ci_test_noimplicitconversions
 add_custom_target(ci_test_diagnostics
     COMMAND CXX=${CLANG_TOOL} ${CMAKE_COMMAND}
     -DCMAKE_BUILD_TYPE=Debug -GNinja
-    -DJSON_BuildTests=ON -DJSON_Diagnostics=ON -DJSON_32bitTest=ON
+    -DJSON_BuildTests=ON -DJSON_Diagnostics=ON -DJSON_32bitTest=AUTO
     -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_diagnostics
     COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_diagnostics
     COMMAND cd ${PROJECT_BINARY_DIR}/build_diagnostics && ${CMAKE_CTEST_COMMAND} --parallel ${N} --output-on-failure
@@ -510,7 +510,7 @@ add_custom_target(ci_test_diagnostics
 add_custom_target(ci_test_legacycomparison
     COMMAND CXX=${CLANG_TOOL} ${CMAKE_COMMAND}
     -DCMAKE_BUILD_TYPE=Debug -GNinja
-    -DJSON_BuildTests=ON -DJSON_LegacyDiscardedValueComparison=ON -DJSON_32bitTest=ON
+    -DJSON_BuildTests=ON -DJSON_LegacyDiscardedValueComparison=ON -DJSON_32bitTest=AUTO
     -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_legacycomparison
     COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_legacycomparison
     COMMAND cd ${PROJECT_BINARY_DIR}/build_legacycomparison && ${CMAKE_CTEST_COMMAND} --parallel ${N} --output-on-failure
@@ -579,7 +579,7 @@ add_custom_target(ci_test_amalgamation
 
     COMMAND CXX=${GCC_TOOL} CXXFLAGS="${GCC_CXXFLAGS}" ${CMAKE_COMMAND}
         -DCMAKE_BUILD_TYPE=Debug -GNinja
-        -DJSON_BuildTests=ON -DJSON_MultipleHeader=OFF -DJSON_FastTests=ON -DJSON_32bitTest=ON
+        -DJSON_BuildTests=ON -DJSON_MultipleHeader=OFF -DJSON_FastTests=ON -DJSON_32bitTest=AUTO
         -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_single_header
     COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_single_header
     COMMAND cd ${PROJECT_BINARY_DIR}/build_single_header && ${CMAKE_CTEST_COMMAND} --parallel ${N} --output-on-failure
@@ -595,7 +595,7 @@ add_custom_target(ci_test_amalgamation
 add_custom_target(ci_test_valgrind
     COMMAND CXX=${GCC_TOOL} ${CMAKE_COMMAND}
         -DCMAKE_BUILD_TYPE=Debug -GNinja
-        -DJSON_BuildTests=ON -DJSON_Valgrind=ON
+        -DJSON_BuildTests=ON -DJSON_Valgrind=ON -DJSON_32bitTest=AUTO
         -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_valgrind
     COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_valgrind
     COMMAND cd ${PROJECT_BINARY_DIR}/build_valgrind && ${CMAKE_CTEST_COMMAND} -L valgrind --parallel ${N} --output-on-failure
@@ -611,7 +611,7 @@ set(CLANG_ANALYZER_CHECKS "fuchsia.HandleChecker,nullability.NullableDereference
 add_custom_target(ci_clang_analyze
     COMMAND CXX=${CLANG_TOOL} ${CMAKE_COMMAND}
         -DCMAKE_BUILD_TYPE=Debug -GNinja
-        -DJSON_BuildTests=ON -DJSON_32bitTest=ON
+        -DJSON_BuildTests=ON -DJSON_32bitTest=AUTO
         -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_clang_analyze
     COMMAND cd ${PROJECT_BINARY_DIR}/build_clang_analyze && ${SCAN_BUILD_TOOL} -enable-checker ${CLANG_ANALYZER_CHECKS} --use-c++=${CLANG_TOOL} -analyze-headers -o ${PROJECT_BINARY_DIR}/report ninja
     COMMENT "Check code with Clang Analyzer"
@@ -743,7 +743,7 @@ add_custom_target(ci_non_git_tests
 add_custom_target(ci_reproducible_tests
     COMMAND ${CMAKE_COMMAND}
         -DCMAKE_BUILD_TYPE=Debug -GNinja
-        -DJSON_BuildTests=ON -DJSON_FastTests=ON
+        -DJSON_BuildTests=ON -DJSON_FastTests=ON -DJSON_32bitTest=AUTO
         -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_reproducible_tests
     COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_reproducible_tests
     COMMAND cd ${PROJECT_BINARY_DIR}/build_reproducible_tests && ${CMAKE_CTEST_COMMAND} --parallel ${N} -LE not_reproducible --output-on-failure
@@ -882,7 +882,7 @@ foreach(COMPILER g++-4.8 g++-4.9 g++-5 g++-6 g++-7 g++-8 g++-9 g++-10 g++-11 cla
         add_custom_target(ci_test_compiler_${COMPILER}
             COMMAND CXX=${COMPILER} ${CMAKE_COMMAND}
                 -DCMAKE_BUILD_TYPE=Debug -GNinja
-                -DJSON_BuildTests=ON -DJSON_FastTests=ON -DJSON_32bitTest=ON
+                -DJSON_BuildTests=ON -DJSON_FastTests=ON -DJSON_32bitTest=AUTO
                 -S${PROJECT_SOURCE_DIR} -B${PROJECT_BINARY_DIR}/build_compiler_${COMPILER}
                 ${ADDITIONAL_FLAGS}
             COMMAND ${CMAKE_COMMAND} --build ${PROJECT_BINARY_DIR}/build_compiler_${COMPILER}
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index 780c065a3..1d0f5a2c3 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -2,9 +2,9 @@ cmake_minimum_required(VERSION 3.13)
 
 option(JSON_Valgrind    "Execute test suite with Valgrind." OFF)
 option(JSON_FastTests   "Skip expensive/slow tests." OFF)
-option(JSON_32bitTest   "Enable the 32bit unit test." OFF)
 
-set(JSON_TestStandards "" CACHE STRING "The list of standards to test explicitly.")
+set(JSON_32bitTest     SAFE_AUTO CACHE STRING "Enable the 32bit unit test (ON/OFF/AUTO/SAFE_AUTO).")
+set(JSON_TestStandards ""        CACHE STRING "The list of standards to test explicitly.")
 
 set(JSON_32BIT_TEST_CXXFLAGS "-m32" CACHE STRING "Compiler flags used to enable 32bit test.")
 set(JSON_32BIT_TEST_LINKFLAGS "-m32" CACHE STRING "Linker flags used to enable 32bit test.")
@@ -133,18 +133,53 @@ foreach(file ${files})
     json_test_add_test_for(${file} MAIN test_main CXX_STANDARDS ${test_cxx_standards} ${test_force})
 endforeach()
 
-if(NOT JSON_32bitTest)
+string(TOUPPER "${JSON_32bitTest}" json_32bit_test)
+if("${json_32bit_test}" STREQUAL AUTO)
+    # check if compiler supports -m32
+    if(${CMAKE_CXX_COMPILER_ID} STREQUAL GNU)
+        execute_process(
+            COMMAND ${CMAKE_CXX_COMPILER} -v --version
+            OUTPUT_VARIABLE gcc_version_output
+            ERROR_VARIABLE gcc_version_output)
+        string(REGEX MATCH "--with-multilib-list=([^ ]*)" multilib_match
+            "${gcc_version_output}")
+        if(multilib_match)
+            string(REPLACE "," ";" multilib_archs "${CMAKE_MATCH_1}")
+            list(FIND multilib_archs m32 has_multilib_m32)
+            if(NOT ${has_multilib_m32} EQUAL -1)
+                message(STATUS "Auto-enabling 32bit unit test.")
+                set(json_32bit_test ON)
+                set(JSON_32BIT_TEST_CXXFLAGS "-m32" CACHE STRING "" FORCE)
+                set(JSON_32BIT_TEST_LINKFLAGS "-m32" CACHE STRING "" FORCE)
+            endif()
+        endif()
+    elseif(${CMAKE_CXX_COMPILER_ID} STREQUAL Clang)
+        execute_process(
+            COMMAND ${CMAKE_CXX_COMPILER} -m32 --version
+            RESULT_VARIABLE clang_version_result
+            OUTPUT_QUIET ERROR_QUIET)
+        if(${clang_version_result} EQUAL 0)
+            message(STATUS "Auto-enabling 32bit unit test.")
+            set(json_32bit_test ON)
+            set(JSON_32BIT_TEST_CXXFLAGS "-m32" CACHE STRING "" FORCE)
+            set(JSON_32BIT_TEST_LINKFLAGS "-m32" CACHE STRING "" FORCE)
+        endif()
+    endif()
+endif()
+
+if("${json_32bit_test}" STREQUAL SAFE_AUTO)
+    # check if compiler is targeting 32bit by default
     include(CheckTypeSize)
     check_type_size("size_t" sizeof_size_t LANGUAGE CXX)
     if(sizeof_size_t AND ${sizeof_size_t} EQUAL 4)
         message(STATUS "Auto-enabling 32bit unit test.")
-        set(JSON_32bitTest ON CACHE BOOL "" FORCE)
+        set(json_32bit_test ON)
         set(JSON_32BIT_TEST_CXXFLAGS "" CACHE STRING "" FORCE)
         set(JSON_32BIT_TEST_LINKFLAGS "" CACHE STRING "" FORCE)
     endif()
 endif()
 
-if(JSON_32bitTest)
+if(${json_32bit_test} STREQUAL ON)
     message(STATUS "Building 32bit unit test.")
     add_library(test_main32 OBJECT ${test_main_SOURCES})
     target_compile_definitions(test_main32 ${test_main_COMPILE_DEFINITIONS})