diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f3dd712..34210f4 100755
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -32,7 +32,6 @@ on:
 
 env:
   CONAN_HOME: "${{ github.workspace }}/conan/"
-  MACOS_MIN_VERSION: 10.15
 
 # https://stackoverflow.com/a/72408109
 concurrency:
@@ -48,8 +47,8 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [windows-latest, macos-latest, ubuntu-latest]
-        r-version: ["3.6.3", "4.0.5", "4.1.3", "4.2.3", "4.3.2"]
+        os: [macos-latest]
+        r-version: ["4.0.5"]
 
     runs-on: ${{ matrix.os }}
 
@@ -83,20 +82,6 @@ jobs:
         extra-packages: any::rcmdcheck
         needs: check
 
-    - name: Generate cache key
-      id: cache-key
-      run: |
-        hash="${{ hashFiles('conanfile.txt', '.github/workflows/ci.yml') }}"
-
-        echo "conan-key=ci-$hash" >> $GITHUB_OUTPUT
-
-    - name: Restore Conan cache
-      id: cache-conan
-      uses: actions/cache/restore@v3
-      with:
-        key: conan-${{ steps.cache-key.outputs.conan-key }}
-        path: ${{ env.CONAN_HOME }}
-
     - name: Build and test package
       uses: r-lib/actions/check-r-package@v2
 
diff --git a/src/Makevars b/src/Makevars
index d749409..fb6d0c5 100644
--- a/src/Makevars
+++ b/src/Makevars
@@ -3,7 +3,6 @@ export CONAN_HOME := $(PWD)/conan-staging/.conan2
 export CC = "$(shell "$(R_HOME)/bin/Rscript" -e 'Sys.which("gcc")')"
 export CXX = "$(shell "$(R_HOME)/bin/Rscript" -e 'Sys.which("g++")')"
 
-
 CONANDEPS_MK := $(shell ../run_conan.py)
 include $(CONANDEPS_MK)
 
@@ -17,3 +16,10 @@ PKG_CPPFLAGS := $(PKG_CPPFLAGS) $(shell "$(R_HOME)/bin/Rscript" -e 'Rcpp:::CxxFl
 PKG_LIBS := $(addprefix -L ,$(CONAN_LIB_DIRS))
 PKG_LIBS := $(PKG_LIBS) $(addprefix -l,$(CONAN_LIBS))
 PKG_LIBS := $(PKG_LIBS) $(addprefix -l,$(CONAN_SYSTEM_LIBS))
+
+OS := $(shell uname 2>/dev/null || echo Unknown)
+
+ifeq ($(OS),Darwin)
+  export MACOSX_DEPLOYMENT_TARGET = 10.15
+  CXXFLAGS += -mmacosx-version-min=10.15
+endif