diff --git a/process.c b/process.c
index 2d842176bd..97ba885fca 100644
--- a/process.c
+++ b/process.c
@@ -5948,7 +5948,7 @@ proc_setgroups(VALUE obj, VALUE ary)
 static VALUE
 proc_initgroups(VALUE obj, VALUE uname, VALUE base_grp)
 {
-    if (initgroups(StringValuePtr(uname), OBJ2GID(base_grp)) != 0) {
+    if (initgroups(StringValueCStr(uname), OBJ2GID(base_grp)) != 0) {
 	rb_sys_fail(0);
     }
     return proc_getgroups(obj);
diff --git a/test/ruby/test_process.rb b/test/ruby/test_process.rb
index 7bd38c8fed..f300444ecc 100644
--- a/test/ruby/test_process.rb
+++ b/test/ruby/test_process.rb
@@ -2339,4 +2339,12 @@ EOS
       assert_equal pid, Timeout.timeout(30) { Process.wait(pid) }
     end;
   end
+
+  if Process.respond_to?(:initgroups)
+    def test_initgroups
+      assert_raise(ArgumentError) do
+        Process.initgroups("\0", 0)
+      end
+    end
+  end
 end