diff --git a/atom.sh b/atom.sh
index 935204bfc..042084751 100755
--- a/atom.sh
+++ b/atom.sh
@@ -26,10 +26,20 @@ esac
 
 export ATOM_DISABLE_SHELLING_OUT_FOR_ENVIRONMENT=true
 
-while getopts ":wtfvh-:" opt; do
+ATOM_ADD=false
+ATOM_NEW_WINDOW=false
+EXIT_CODE_OVERRIDE=
+
+while getopts ":anwtfvh-:" opt; do
   case "$opt" in
     -)
       case "${OPTARG}" in
+        add)
+          ATOM_ADD=true
+          ;;
+        new-window)
+          ATOM_NEW_WINDOW=true
+          ;;
         wait)
           WAIT=1
           ;;
@@ -45,6 +55,12 @@ while getopts ":wtfvh-:" opt; do
           ;;
       esac
       ;;
+    a)
+      ATOM_ADD=true
+      ;;
+    n)
+      ATOM_NEW_WINDOW=true
+      ;;
     w)
       WAIT=1
       ;;
@@ -58,6 +74,11 @@ while getopts ":wtfvh-:" opt; do
   esac
 done
 
+if [ "${ATOM_ADD}" = "true" ] && [ "${ATOM_NEW_WINDOW}" = "true" ]; then
+  EXPECT_OUTPUT=1
+  EXIT_CODE_OVERRIDE=1
+fi
+
 if [ $REDIRECT_STDERR ]; then
   exec 2> /dev/null
 fi
@@ -115,7 +136,11 @@ if [ $OS == 'Mac' ]; then
 
   if [ $EXPECT_OUTPUT ]; then
     "$ATOM_PATH/$ATOM_APP_NAME/Contents/MacOS/$ATOM_EXECUTABLE_NAME" --executed-from="$(pwd)" --pid=$$ "$@"
-    exit $?
+    if [ $? -eq 0 ] && [ -n "${EXIT_CODE_OVERRIDE}" ]; then
+      exit "${EXIT_CODE_OVERRIDE}"
+    else
+      exit $?
+    fi
   else
     open -a "$ATOM_PATH/$ATOM_APP_NAME" -n --args --executed-from="$(pwd)" --pid=$$ --path-environment="$PATH" "$@"
   fi
@@ -144,7 +169,11 @@ elif [ $OS == 'Linux' ]; then
 
   if [ $EXPECT_OUTPUT ]; then
     "$ATOM_PATH" --executed-from="$(pwd)" --pid=$$ "$@"
-    exit $?
+    if [ $? -eq 0 ] && [ -n "${EXIT_CODE_OVERRIDE}" ]; then
+      exit "${EXIT_CODE_OVERRIDE}"
+    else
+      exit $?
+    fi
   else
     (
     nohup "$ATOM_PATH" --executed-from="$(pwd)" --pid=$$ "$@" > "$ATOM_HOME/nohup.out" 2>&1
diff --git a/src/main-process/parse-command-line.js b/src/main-process/parse-command-line.js
index d57a2fca5..27a2f07f6 100644
--- a/src/main-process/parse-command-line.js
+++ b/src/main-process/parse-command-line.js
@@ -105,6 +105,16 @@ module.exports = function parseCommandLine (processArgs) {
     executedFrom = process.cwd()
   }
 
+  if (newWindow && addToLastWindow) {
+    process.stderr.write(
+      `Only one of the --add and --new-window options may be specified at the same time.\n\n${options.help()}`,
+    )
+
+    // Exiting the main process with a nonzero exit code on MacOS causes the app open to fail with the mysterious
+    // message "LSOpenURLsWithRole() failed for the application /Applications/Atom Dev.app with error -10810."
+    process.exit(0)
+  }
+
   let pidToKillWhenClosed = null
   if (args['wait']) {
     pidToKillWhenClosed = args['pid']