diff --git a/lib.sh b/lib.sh
index 0c15045..71a7b58 100755
--- a/lib.sh
+++ b/lib.sh
@@ -138,23 +138,28 @@ function get_tar_relpath {
 ###############################################################################
 # Updates APT package lists if they are stale (modified more than 5 minutes ago).
 # This ensures compatibility with environments like nektos/act where package lists
-# may be empty or stale.
+# may be empty or stale. Only runs when ACT environment variable is set (nektos/act)
+# to avoid slowing down normal GitHub Actions runs.
 # Arguments:
 #   None
 # Returns:
 #   None
 ###############################################################################
 function update_apt_lists_if_stale {
-  if [[ -z "$(find -H /var/lib/apt/lists -maxdepth 0 -mmin -5 2>/dev/null)" ]]; then
-    log "APT package lists are stale, updating..."
-    if command -v apt-fast > /dev/null 2>&1; then
-      sudo apt-fast update > /dev/null 2>&1 || sudo apt update > /dev/null 2>&1 || true
+  # Only check for stale package lists when running in nektos/act
+  # GitHub Actions runners have fresh package lists, so skip this overhead
+  if [ "${ACT}" = "true" ]; then
+    if [[ -z "$(find -H /var/lib/apt/lists -maxdepth 0 -mmin -5 2>/dev/null)" ]]; then
+      log "APT package lists are stale, updating..."
+      if command -v apt-fast > /dev/null 2>&1; then
+        sudo apt-fast update > /dev/null 2>&1 || sudo apt update > /dev/null 2>&1 || true
+      else
+        sudo apt update > /dev/null 2>&1 || true
+      fi
+      log "APT package lists updated"
     else
-      sudo apt update > /dev/null 2>&1 || true
+      log "APT package lists are fresh (within 5 minutes), skipping update"
     fi
-    log "APT package lists updated"
-  else
-    log "APT package lists are fresh (within 5 minutes), skipping update"
   fi
 }