diff --git a/libexec/rbenv-init b/libexec/rbenv-init
index 8e6ee3d8..7ddae5e5 100755
--- a/libexec/rbenv-init
+++ b/libexec/rbenv-init
@@ -33,9 +33,9 @@ done
 
 shell="$1"
 if [ -z "$shell" ]; then
-  shell="$(ps c -p "$PPID" -o 'ucomm=' 2>/dev/null || true)"
-  shell="${shell##-}"
+  shell="$(ps -p "$PPID" -o 'args=' 2>/dev/null || true)"
   shell="${shell%% *}"
+  shell="${shell##-}"
   shell="${shell:-$SHELL}"
   shell="${shell##*/}"
 fi
diff --git a/test/init.bats b/test/init.bats
index 0a46dd0d..d7005489 100644
--- a/test/init.bats
+++ b/test/init.bats
@@ -25,12 +25,24 @@ load test_helper
 }
 
 @test "detect parent shell" {
-  root="$(cd $BATS_TEST_DIRNAME/.. && pwd)"
   SHELL=/bin/false run rbenv-init -
   assert_success
   assert_line "export RBENV_SHELL=bash"
 }
 
+@test "detect parent shell from script" {
+  mkdir -p "$RBENV_TEST_DIR"
+  cd "$RBENV_TEST_DIR"
+  cat > myscript.sh <<OUT
+#!/bin/sh
+eval "\$(rbenv-init -)"
+echo \$RBENV_SHELL
+OUT
+  chmod +x myscript.sh
+  run ./myscript.sh /bin/zsh
+  assert_success "sh"
+}
+
 @test "setup shell completions (fish)" {
   root="$(cd $BATS_TEST_DIRNAME/.. && pwd)"
   run rbenv-init - fish