diff --git a/.github/workflows/R-CMD-check.yaml b/.github/workflows/R-CMD-check.yaml
index 85f47ef..b24a376 100644
--- a/.github/workflows/R-CMD-check.yaml
+++ b/.github/workflows/R-CMD-check.yaml
@@ -27,7 +27,7 @@ jobs:
       R_KEEP_PKG_SOURCE: yes
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
 
       - uses: r-lib/actions/setup-pandoc@v2
 
diff --git a/R/write_xlsx.R b/R/write_xlsx.R
index 59a5511..d019a41 100644
--- a/R/write_xlsx.R
+++ b/R/write_xlsx.R
@@ -54,6 +54,9 @@ normalize_df <- function(df){
   for(i in which(vapply(df, inherits, logical(1), c("factor", "hms")))){
     df[[i]] <- as.character(df[[i]])
   }
+  for(i in which(vapply(df, function(x){is.integer(x) && inherits(x, "POSIXct")}, logical(1)))){
+    df[[i]] <- as.POSIXct(as.double(df[[i]]))
+  }
   for(i in which(vapply(df, inherits, logical(1), "POSIXlt"))){
     df[[i]] <- as.POSIXct(df[[i]])
   }
diff --git a/appveyor.yml b/appveyor.yml
deleted file mode 100644
index acebe36..0000000
--- a/appveyor.yml
+++ /dev/null
@@ -1,50 +0,0 @@
-# DO NOT CHANGE the "init" and "install" sections below
-
-# Download script file from GitHub
-init:
-  ps: |
-        $ErrorActionPreference = "Stop"
-        Invoke-WebRequest http://raw.github.com/krlmlr/r-appveyor/master/scripts/appveyor-tool.ps1 -OutFile "..\appveyor-tool.ps1"
-        Import-Module '..\appveyor-tool.ps1'
-
-install:
-  ps: Bootstrap
-
-cache:
-  - C:\RLibrary
-
-# Adapt as necessary starting from here
-
-environment:
-  matrix:
-    - R_VERSION: 3.6.3
-    - R_VERSION: patched
-
-build_script:
-  - travis-tool.sh install_deps
-
-test_script:
-  - travis-tool.sh run_tests
-
-on_failure:
-  - 7z a failure.zip *.Rcheck\*
-  - appveyor PushArtifact failure.zip
-
-artifacts:
-  - path: '*.Rcheck\**\*.log'
-    name: Logs
-
-  - path: '*.Rcheck\**\*.out'
-    name: Logs
-
-  - path: '*.Rcheck\**\*.fail'
-    name: Logs
-
-  - path: '*.Rcheck\**\*.Rout'
-    name: Logs
-
-  - path: '\*_*.tar.gz'
-    name: Bits
-
-  - path: '\*_*.zip'
-    name: Bits