diff --git a/.github/workflows/R-CMD-check.yaml b/.github/workflows/R-CMD-check.yaml
index c984aa4..8ce0323 100644
--- a/.github/workflows/R-CMD-check.yaml
+++ b/.github/workflows/R-CMD-check.yaml
@@ -43,6 +43,14 @@ jobs:
         with:
           extra-packages: rcmdcheck
 
+      - name: Set CRAN mirror
+        run: echo "options(repos = c(CRAN='https://cloud.r-project.org/'))" > ~/.Rprofile
+
+      - name: Install lme4 from source to fix Matrix errors
+        run: | 
+          install.packages('lme4', type = 'source')
+        shell: Rscript {0}
+        
       - uses: r-lib/actions/check-r-package@v2
 
       - name: Show testthat output