diff --git a/io.c b/io.c
index 92fe5322da..a78936488f 100644
--- a/io.c
+++ b/io.c
@@ -8038,7 +8038,7 @@ popen_finish(VALUE port, VALUE klass)
     if (NIL_P(port)) {
         /* child */
         if (rb_block_given_p()) {
-            rb_yield(Qnil);
+            rb_protect(rb_yield, Qnil, NULL);
             rb_io_flush(rb_ractor_stdout());
             rb_io_flush(rb_ractor_stderr());
             _exit(0);
diff --git a/test/ruby/test_process.rb b/test/ruby/test_process.rb
index 7057e0b837..9c1836dffb 100644
--- a/test/ruby/test_process.rb
+++ b/test/ruby/test_process.rb
@@ -922,15 +922,29 @@ class TestProcess < Test::Unit::TestCase
     }
   end
 
-  def test_popen_fork
-    IO.popen("-") {|io|
-      if !io
-        puts "fooo"
-      else
-        assert_equal("fooo\n", io.read)
+  if Process.respond_to?(:fork)
+    def test_popen_fork
+      IO.popen("-") do |io|
+        if !io
+          puts "fooo"
+        else
+          assert_equal("fooo\n", io.read)
+        end
       end
-    }
-  rescue NotImplementedError
+    end
+
+    def test_popen_fork_ensure
+      IO.popen("-") do |io|
+        if !io
+          STDERR.reopen(STDOUT)
+          raise "fooo"
+        else
+          assert_empty io.read
+        end
+      end
+    rescue RuntimeError
+      abort "[Bug #20995] should not reach here"
+    end
   end
 
   def test_fd_inheritance