diff --git a/.travis.yml b/.travis.yml
index 0a2030665..07d4afadd 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -37,7 +37,7 @@ matrix:
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test']
-        packages: [g++-4.9, valgrind]
+        packages: ['g++-4.9', 'valgrind', 'ninja-build']
 
   # clang sanitizer
   - os: linux
@@ -48,7 +48,7 @@ matrix:
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test', 'llvm-toolchain-trusty-5.0']
-        packages: ['g++-6', 'clang-5.0']
+        packages: ['g++-6', 'clang-5.0', 'ninja-build']
 
   # cppcheck
   - os: linux
@@ -59,7 +59,7 @@ matrix:
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test']
-        packages: [g++-4.9, cppcheck]
+        packages: ['g++-4.9', 'cppcheck', 'ninja-build']
     after_success:
       - make cppcheck
 
@@ -73,7 +73,7 @@ matrix:
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test']
-        packages: [g++-4.9, cppcheck]
+        packages: ['g++-4.9', 'cppcheck', 'ninja-build']
     after_success:
       - make clean
       - CPPFLAGS="-DJSON_NOEXCEPTION" make check TEST_PATTERN="-e \"*\""
@@ -85,7 +85,7 @@ matrix:
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test']
-        packages: ['g++-4.9', 'ruby']
+        packages: ['g++-4.9', 'ruby', 'ninja-build']
     before_script:
       - wget http://ftp.de.debian.org/debian/pool/main/l/lcov/lcov_1.11.orig.tar.gz
       - tar xf lcov_1.11.orig.tar.gz
@@ -113,7 +113,7 @@ matrix:
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test', 'llvm-toolchain-precise-3.6']
-        packages: ['g++-6', 'clang-3.6']
+        packages: ['g++-6', 'clang-3.6', 'ninja-build']
       coverity_scan:
         project:
           name: "nlohmann/json"
@@ -157,7 +157,7 @@ matrix:
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test']
-        packages: g++-4.9
+        packages: ['g++-4.9', 'ninja-build']
 
   - os: linux
     compiler: gcc
@@ -165,7 +165,7 @@ matrix:
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test']
-        packages: g++-5
+        packages: ['g++-5', 'ninja-build']
 
   - os: linux
     compiler: gcc
@@ -173,7 +173,7 @@ matrix:
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test']
-        packages: g++-6
+        packages: ['g++-6', 'ninja-build']
 
   - os: linux
     compiler: gcc
@@ -181,7 +181,7 @@ matrix:
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test']
-        packages: g++-7
+        packages: ['g++-7', 'ninja-build']
 
   - os: linux
     compiler: gcc
@@ -191,7 +191,7 @@ matrix:
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test']
-        packages: g++-7
+        packages: ['g++-7', 'ninja-build']
 
   # Linux / Clang
 
@@ -201,7 +201,7 @@ matrix:
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test', 'llvm-toolchain-precise-3.5']
-        packages: ['g++-6', 'clang-3.5']
+        packages: ['g++-6', 'clang-3.5', 'ninja-build']
 
   - os: linux
     compiler: clang
@@ -209,7 +209,7 @@ matrix:
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test', 'llvm-toolchain-precise-3.6']
-        packages: ['g++-6', 'clang-3.6']
+        packages: ['g++-6', 'clang-3.6', 'ninja-build']
 
   - os: linux
     compiler: clang
@@ -217,7 +217,7 @@ matrix:
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test', 'llvm-toolchain-precise-3.7']
-        packages: ['g++-6', 'clang-3.7']
+        packages: ['g++-6', 'clang-3.7', 'ninja-build']
 
   - os: linux
     compiler: clang
@@ -225,7 +225,7 @@ matrix:
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test']
-        packages: ['g++-6', 'clang-3.8']
+        packages: ['g++-6', 'clang-3.8', 'ninja-build']
 
   - os: linux
     compiler: clang
@@ -233,7 +233,7 @@ matrix:
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test']
-        packages: ['g++-6', 'clang-3.9']
+        packages: ['g++-6', 'clang-3.9', 'ninja-build']
 
   - os: linux
     compiler: clang
@@ -241,7 +241,7 @@ matrix:
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test', 'llvm-toolchain-trusty-4.0']
-        packages: ['g++-6', 'clang-4.0']
+        packages: ['g++-6', 'clang-4.0', 'ninja-build']
 
   - os: linux
     compiler: clang
@@ -249,7 +249,7 @@ matrix:
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test', 'llvm-toolchain-trusty-5.0']
-        packages: ['g++-6', 'clang-5.0']
+        packages: ['g++-6', 'clang-5.0', 'ninja-build']
 
   - os: linux
     compiler: clang
@@ -259,7 +259,7 @@ matrix:
     addons:
       apt:
         sources: ['ubuntu-toolchain-r-test', 'llvm-toolchain-trusty-5.0']
-        packages: ['g++-6', 'clang-5.0']
+        packages: ['g++-6', 'clang-5.0', 'ninja-build']
 
 ################
 # build script #
@@ -268,9 +268,9 @@ matrix:
 script:
   # get CMake (only for systems with brew - macOS)
   - |
-     if [[ !(-x $(which cmake)) && (-x $(which brew)) ]]; then
+     if [[ (-x $(which brew)) ]]; then
        brew update
-       brew install cmake
+       brew install cmake ninja
        cmake --version
      fi
 
@@ -283,7 +283,7 @@ script:
 
   # compile and execute unit tests
   - mkdir -p build && cd build
-  - cmake .. ${CMAKE_OPTIONS} && cmake --build . --config Release -- -j4
+  - cmake .. ${CMAKE_OPTIONS} -GNinja && cmake --build . --config Release
   - ctest -C Release -V
   - cd ..