diff --git a/src/jsontestrunner/CMakeLists.txt b/src/jsontestrunner/CMakeLists.txt
index 39c6f4871..210e0900b 100644
--- a/src/jsontestrunner/CMakeLists.txt
+++ b/src/jsontestrunner/CMakeLists.txt
@@ -1,4 +1,13 @@
-find_package(PythonInterp 2.6)
+if(CMAKE_VERSION VERSION_GREATER_EQUAL 3.12.0)
+  # The new Python3 module is much more robust than the previous PythonInterp
+  find_package (Python3 COMPONENTS Interpreter)
+  # Set variables for backwards compatibility with cmake < 3.12.0
+  set(PYTHONINTERP_FOUND ${Python3_Interpreter_FOUND})
+  set(PYTHON_EXECUTABLE ${Python3_EXECUTABLE})
+else()
+  set(Python_ADDITIONAL_VERSIONS 3.8)
+  find_package(PythonInterp 3)
+endif()
 
 add_executable(jsontestrunner_exe
                main.cpp
diff --git a/src/test_lib_json/main.cpp b/src/test_lib_json/main.cpp
index 1d636d8a0..ad34c8ae9 100644
--- a/src/test_lib_json/main.cpp
+++ b/src/test_lib_json/main.cpp
@@ -350,7 +350,7 @@ JSONTEST_FIXTURE_LOCAL(ValueTest, arrayInsertAtRandomIndex) {
   JSONTEST_ASSERT_EQUAL(Json::Value("index1"), array[2]);
   JSONTEST_ASSERT_EQUAL(Json::Value("index2"), array[3]);
   // checking address
-  for (int i = 0; i < 3; i++) {
+  for (Json::ArrayIndex i = 0; i < 3; i++) {
     JSONTEST_ASSERT_EQUAL(vec[i], &array[i]);
   }
   vec.push_back(&array[3]);
@@ -362,7 +362,7 @@ JSONTEST_FIXTURE_LOCAL(ValueTest, arrayInsertAtRandomIndex) {
   JSONTEST_ASSERT_EQUAL(Json::Value("index1"), array[3]);
   JSONTEST_ASSERT_EQUAL(Json::Value("index2"), array[4]);
   // checking address
-  for (int i = 0; i < 4; i++) {
+  for (Json::ArrayIndex i = 0; i < 4; i++) {
     JSONTEST_ASSERT_EQUAL(vec[i], &array[i]);
   }
   vec.push_back(&array[4]);
@@ -376,7 +376,7 @@ JSONTEST_FIXTURE_LOCAL(ValueTest, arrayInsertAtRandomIndex) {
   JSONTEST_ASSERT_EQUAL(Json::Value("index2"), array[4]);
   JSONTEST_ASSERT_EQUAL(Json::Value("index5"), array[5]);
   // checking address
-  for (int i = 0; i < 5; i++) {
+  for (Json::ArrayIndex i = 0; i < 5; i++) {
     JSONTEST_ASSERT_EQUAL(vec[i], &array[i]);
   }
   vec.push_back(&array[5]);
@@ -2234,7 +2234,6 @@ JSONTEST_FIXTURE_LOCAL(StyledStreamWriterTest, writeNestedObjects) {
 }
 
 JSONTEST_FIXTURE_LOCAL(StyledStreamWriterTest, multiLineArray) {
-  Json::StyledStreamWriter writer;
   {
     // Array member has more than 20 print effect rendering lines
     const Json::String expected("[\n\t0,"
@@ -2268,6 +2267,7 @@ JSONTEST_FIXTURE_LOCAL(StyledStreamWriterTest, multiLineArray) {
     JSONTEST_ASSERT_STRING_EQUAL(expected, result);
   }
   {
+    Json::StyledStreamWriter writer;
     // Array members do not exceed 21 print effects to render a single line
     const Json::String expected("[ 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 ]\n");
     Json::Value root;