diff --git a/.ci/azure-build.yml b/.ci/azure-build.yml
index e6b37f8e..b7cb5bb5 100644
--- a/.ci/azure-build.yml
+++ b/.ci/azure-build.yml
@@ -5,7 +5,7 @@ steps:
     cmakeArgs: .. -DCLI11_SINGLE_FILE=$(cli11.single) -DCLI11_CXX_STD=$(cli11.std) -DCLI11_SINGLE_FILE_TESTS=$(cli11.single) -DCMAKE_BUILD_TYPE=$(cli11.build_type) $(cli11.options)
   displayName: 'Configure'
 
-- script: cmake --build . $(cli11.threadopt)
+- script: cmake --build .
   displayName: 'Build'
   workingDirectory: build
 
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 8b950705..020d7cf3 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -11,6 +11,9 @@ else()
     cmake_policy(VERSION 3.14)
 endif()
 
+# TESTING: remove this later
+set_property(GLOBAL PROPERTY RULE_LAUNCH_COMPILE "${CMAKE_COMMAND} -E time")
+
 set(VERSION_REGEX "#define CLI11_VERSION[ \t]+\"(.+)\"")
 
 # Read in the line containing the version
diff --git a/azure-pipelines.yml b/azure-pipelines.yml
index 0c2f5baf..45840db3 100644
--- a/azure-pipelines.yml
+++ b/azure-pipelines.yml
@@ -11,7 +11,7 @@ variables:
   cli11.std: 14
   cli11.build_type: Debug
   cli11.options:
-  cli11.threadopt: -j
+  CMAKE_BUILD_PARALLEL_LEVEL: 4
 
 jobs:
 
@@ -21,7 +21,7 @@ jobs:
     cli11.options: -DCLANG_TIDY_FIX=ON
     cli11.std: 11
     cli11.single: OFF
-    cli11.threadopt:
+    CMAKE_BUILD_PARALLEL_LEVEL: 1
   pool:
     vmImage: 'ubuntu-16.04'
   container: silkeh/clang:5
@@ -37,9 +37,9 @@ jobs:
   strategy:
     matrix:
       Linux:
-        vmImage: 'ubuntu-16.04'
+        vmImage: 'ubuntu-latest'
       macOS:
-        vmImage: 'macOS-10.14'
+        vmImage: 'macOS-latest'
       Windows:
         vmImage: 'vs2017-win2016'
   pool:
@@ -52,7 +52,7 @@ jobs:
   variables:
     cli11.single: OFF
   pool:
-    vmImage: 'ubuntu-16.04'
+    vmImage: 'ubuntu-latest'
   strategy:
     matrix:
       gcc9:
diff --git a/include/CLI/Optional.hpp b/include/CLI/Optional.hpp
index 6e60fb60..510af3b3 100644
--- a/include/CLI/Optional.hpp
+++ b/include/CLI/Optional.hpp
@@ -8,30 +8,35 @@
 #include "CLI/Macros.hpp"
 
 // [CLI11:verbatim]
-#ifdef __has_include
 
 // You can explicitly enable or disable support
-// by defining these to 1 or 0.
-#if defined(CLI11_CPP17) && __has_include(<optional>) && \
-     !defined(CLI11_STD_OPTIONAL)
+// by defining to 1 or 0. Extra check here to ensure it's in the stdlib too.
+// We nest the check for __has_include and it's usage
+#ifndef CLI11_STD_OPTIONAL
+#ifdef __has_include
+#if defined(CLI11_CPP17) && __has_include(<optional>)
 #define CLI11_STD_OPTIONAL 1
-#elif !defined(CLI11_STD_OPTIONAL)
+#else
 #define CLI11_STD_OPTIONAL 0
 #endif
+#else
+#define CLI11_STD_OPTIONAL 0
+#endif
+#endif
 
-#if !defined(CLI11_EXPERIMENTAL_OPTIONAL)
+#ifndef CLI11_EXPERIMENTAL_OPTIONAL
 #define CLI11_EXPERIMENTAL_OPTIONAL 0
 #endif
 
-#if __has_include(<boost/optional.hpp>) && !defined(CLI11_BOOST_OPTIONAL)
-#include <boost/version.hpp>
-#if BOOST_VERSION >= 106100
-#define CLI11_BOOST_OPTIONAL 1
-#endif
-#elif !defined(CLI11_BOOST_OPTIONAL)
+#ifndef CLI11_BOOST_OPTIONAL
 #define CLI11_BOOST_OPTIONAL 0
 #endif
 
+#if CLI11_BOOST_OPTIONAL
+#include <boost/version.hpp>
+#if BOOST_VERSION < 106100
+#error "This boost::optional version is not supported, use 1.61 or better"
+#endif
 #endif
 
 #if CLI11_STD_OPTIONAL
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index ec1f931a..460a315e 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -115,15 +115,15 @@ file(WRITE "${PROJECT_BINARY_DIR}/CTestCustom.cmake"
 find_package(Boost 1.61)
 if(Boost_FOUND)
     if(TARGET Boost::boost)
-        target_link_libraries(informational PUBLIC Boost::boost)
-        target_link_libraries(OptionalTest PUBLIC Boost::boost)
+        target_link_libraries(informational PRIVATE Boost::boost)
+        target_link_libraries(OptionalTest PRIVATE Boost::boost)
     else()
-        target_include_directories(informational PUBLIC ${Boost_INCLUDE_DIRS})
-        target_include_directories(OptionalTest PUBLIC ${Boost_INCLUDE_DIRS})
+        target_include_directories(informational PRIVATE ${Boost_INCLUDE_DIRS})
+        target_include_directories(OptionalTest PRIVATE ${Boost_INCLUDE_DIRS})
     endif()
-    # Enforce Boost::Optional even if __has_include is missing on your compiler
-    target_compile_definitions(informational PUBLIC CLI11_BOOST_OPTIONAL)
-    target_compile_definitions(OptionalTest PUBLIC CLI11_BOOST_OPTIONAL)
+
+    target_compile_definitions(informational PRIVATE CLI11_BOOST_OPTIONAL)
+    target_compile_definitions(OptionalTest PRIVATE CLI11_BOOST_OPTIONAL)
 endif()
 
 if(CMAKE_BUILD_TYPE STREQUAL Coverage)