diff --git a/.github/workflows/cmake.yml b/.github/workflows/cmake.yml
index 6665cdea..57e99443 100644
--- a/.github/workflows/cmake.yml
+++ b/.github/workflows/cmake.yml
@@ -13,7 +13,7 @@ jobs:
       # Don't cancel the macOS build if the Linux build fails, etc.
       fail-fast: false
       matrix:
-        os: [ubuntu-18.04, macos-10.15]
+        os: [ubuntu-20.04, macos-10.15]
 
     steps:
     - uses: actions/checkout@v2
diff --git a/3rdparty/json b/3rdparty/json
index bbdb29c6..0db99d5e 160000
--- a/3rdparty/json
+++ b/3rdparty/json
@@ -1 +1 @@
-Subproject commit bbdb29c6583e9e68f7f2bdce59a7384f061e0e32
+Subproject commit 0db99d5ed1ba0c4409509db3916e7bd8398ee920
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 9e831265..cfbf63b8 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -126,7 +126,8 @@ endif (MSVC)
 
 # 10.9: minimum version that supports unordered_map
 # 10.14: required by tbb 2021.3.0 (due to use of alignas)
-set(CMAKE_OSX_DEPLOYMENT_TARGET 10.14)
+# 10.15: required by std::filesytstem
+set(CMAKE_OSX_DEPLOYMENT_TARGET 10.15)
 
 find_package(TBB REQUIRED)