diff --git a/.travis.yml b/.travis.yml
index ef6c24b5..bf749c1e 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -145,6 +145,11 @@ matrix:
   - os: osx
     osx_image: xcode12
 
+  - os: osx
+    osx_image: xcode12
+    env:
+      - IMPLICIT_CONVERSIONS=OFF
+
   # Linux / GCC
 
   - os: linux
@@ -203,6 +208,16 @@ matrix:
         sources: ['ubuntu-toolchain-r-test']
         packages: ['g++-9', 'ninja-build']
 
+  - os: linux
+    compiler: gcc
+    env:
+      - COMPILER=g++-9
+      - IMPLICIT_CONVERSIONS=OFF
+    addons:
+      apt:
+        sources: ['ubuntu-toolchain-r-test']
+        packages: ['g++-9', 'ninja-build']
+
   - os: linux
     compiler: gcc
     env:
@@ -315,10 +330,12 @@ script:
   - if [[ "${COMPILER}" != "" ]]; then export CXX=${COMPILER}; fi
   # by default, use the single-header version
   - if [[ "${MULTIPLE_HEADERS}" == "" ]]; then export MULTIPLE_HEADERS=OFF; fi
+  # by default, use implicit conversions
+  - if [[ "${IMPLICIT_CONVERSIONS}" == "" ]]; then export IMPLICIT_CONVERSIONS=ON; fi
 
   # compile and execute unit tests
   - mkdir -p build && cd build
-  - cmake .. ${CMAKE_OPTIONS} -DJSON_MultipleHeaders=${MULTIPLE_HEADERS} -DJSON_BuildTests=On -GNinja && cmake --build . --config Release
+  - cmake .. ${CMAKE_OPTIONS} -DJSON_MultipleHeaders=${MULTIPLE_HEADERS} -DJSON_ImplicitConversions=${IMPLICIT_CONVERSIONS} -DJSON_BuildTests=On -GNinja && cmake --build . --config Release
   - ctest -C Release --timeout 2700 -V -j
   - cd ..
 
diff --git a/appveyor.yml b/appveyor.yml
index 73788956..5836f88d 100644
--- a/appveyor.yml
+++ b/appveyor.yml
@@ -7,6 +7,7 @@ environment:
       platform: x86
       CXX_FLAGS: ""
       LINKER_FLAGS: ""
+      CMAKE_OPTIONS: ""
       GENERATOR: Visual Studio 14 2015
 
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
@@ -14,6 +15,7 @@ environment:
       platform: x86
       CXX_FLAGS: ""
       LINKER_FLAGS: ""
+      CMAKE_OPTIONS: ""
       GENERATOR: Visual Studio 15 2017
 
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
@@ -21,6 +23,7 @@ environment:
       platform: x86
       CXX_FLAGS: ""
       LINKER_FLAGS: ""
+      CMAKE_OPTIONS: ""
       GENERATOR: Visual Studio 16 2019
 
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
@@ -28,6 +31,7 @@ environment:
       platform: x64
       CXX_FLAGS: ""
       LINKER_FLAGS: ""
+      CMAKE_OPTIONS: ""
       GENERATOR: Visual Studio 16 2019
 
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
@@ -36,6 +40,7 @@ environment:
       platform: x86
       CXX_FLAGS: ""
       LINKER_FLAGS: ""
+      CMAKE_OPTIONS: ""
       GENERATOR: Ninja
 
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
@@ -44,6 +49,7 @@ environment:
       platform: x86
       CXX_FLAGS: ""
       LINKER_FLAGS: ""
+      CMAKE_OPTIONS: ""
       GENERATOR: Ninja
 
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
@@ -51,6 +57,7 @@ environment:
       platform: x86
       CXX_FLAGS: ""
       LINKER_FLAGS: ""
+      CMAKE_OPTIONS: ""
       GENERATOR: Visual Studio 14 2015
 
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
@@ -59,6 +66,7 @@ environment:
       name: with_win_header
       CXX_FLAGS: ""
       LINKER_FLAGS: ""
+      CMAKE_OPTIONS: ""
       GENERATOR: Visual Studio 14 2015
 
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
@@ -66,6 +74,7 @@ environment:
       platform: x86
       CXX_FLAGS: "/permissive- /std:c++latest /utf-8"
       LINKER_FLAGS: ""
+      CMAKE_OPTIONS: ""
       GENERATOR: Visual Studio 15 2017
 
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
@@ -73,6 +82,15 @@ environment:
       platform: x86
       CXX_FLAGS: ""
       LINKER_FLAGS: ""
+      CMAKE_OPTIONS: "-DJSON_ImplicitConversions=OFF"
+      GENERATOR: Visual Studio 16 2019
+
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
+      configuration: Release
+      platform: x64
+      CXX_FLAGS: ""
+      LINKER_FLAGS: ""
+      CMAKE_OPTIONS: ""
       GENERATOR: Visual Studio 16 2019
 
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2015
@@ -80,6 +98,7 @@ environment:
       platform: x64
       CXX_FLAGS: ""
       LINKER_FLAGS: ""
+      CMAKE_OPTIONS: ""
       GENERATOR: Visual Studio 14 2015
 
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
@@ -87,6 +106,7 @@ environment:
       platform: x64
       CXX_FLAGS: "/permissive- /std:c++latest /Zc:__cplusplus /utf-8 /F4000000"
       LINKER_FLAGS: "/STACK:4000000"
+      CMAKE_OPTIONS: ""
       GENERATOR: Visual Studio 15 2017
 
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
@@ -94,6 +114,7 @@ environment:
       platform: x64
       CXX_FLAGS: ""
       LINKER_FLAGS: ""
+      CMAKE_OPTIONS: ""
       GENERATOR: Visual Studio 16 2019
 
 init:
@@ -112,7 +133,7 @@ before_build:
   # for with_win_header build, inject the inclusion of Windows.h to the single-header library
   - ps: if ($env:name -Eq "with_win_header") { $header_path = "single_include\nlohmann\json.hpp" }
   - ps: if ($env:name -Eq "with_win_header") { "#include <Windows.h>`n" + (Get-Content $header_path | Out-String) | Set-Content $header_path }
-  - if "%GENERATOR%"=="Ninja" (cmake . -G "%GENERATOR%" -DCMAKE_BUILD_TYPE="%configuration%" -DCMAKE_CXX_FLAGS="%CXX_FLAGS%" -DCMAKE_EXE_LINKER_FLAGS="%LINKER_FLAGS%" -DCMAKE_IGNORE_PATH="C:/Program Files/Git/usr/bin" -DJSON_BuildTests=On) else (cmake . -G "%GENERATOR%" -A "%GENERATOR_PLATFORM%" -DCMAKE_CXX_FLAGS="%CXX_FLAGS%" -DCMAKE_EXE_LINKER_FLAGS="%LINKER_FLAGS%" -DCMAKE_IGNORE_PATH="C:/Program Files/Git/usr/bin" -DJSON_BuildTests=On)
+  - if "%GENERATOR%"=="Ninja" (cmake . -G "%GENERATOR%" -DCMAKE_BUILD_TYPE="%configuration%" -DCMAKE_CXX_FLAGS="%CXX_FLAGS%" -DCMAKE_EXE_LINKER_FLAGS="%LINKER_FLAGS%" -DCMAKE_IGNORE_PATH="C:/Program Files/Git/usr/bin" -DJSON_BuildTests=On "%CMAKE_OPTIONS%") else (cmake . -G "%GENERATOR%" -A "%GENERATOR_PLATFORM%" -DCMAKE_CXX_FLAGS="%CXX_FLAGS%" -DCMAKE_EXE_LINKER_FLAGS="%LINKER_FLAGS%" -DCMAKE_IGNORE_PATH="C:/Program Files/Git/usr/bin" -DJSON_BuildTests=On "%CMAKE_OPTIONS%")
 
 build_script:
   - cmake --build . --config "%configuration%"