diff --git a/testcases/complete-run.pl b/testcases/complete-run.pl
index e85f5bbb..56ed01a5 100755
--- a/testcases/complete-run.pl
+++ b/testcases/complete-run.pl
@@ -24,10 +24,15 @@ use StartXDummy;
 use StatusLine;
 # the following modules are not shipped with Perl
 use AnyEvent;
+use AnyEvent::Util;
 use AnyEvent::Handle;
 use AnyEvent::I3 qw(:all);
 use X11::XCB;
 
+# Close superfluous file descriptors which were passed by running in a VIM
+# subshell or situations like that.
+AnyEvent::Util::close_all_fds_except(0, 1, 2);
+
 # We actually use AnyEvent to make sure it loads an event loop implementation.
 # Afterwards, we overwrite SIGCHLD:
 my $cv = AnyEvent->condvar;
diff --git a/testcases/lib/SocketActivation.pm b/testcases/lib/SocketActivation.pm
index 01b1eb3d..da1dda33 100644
--- a/testcases/lib/SocketActivation.pm
+++ b/testcases/lib/SocketActivation.pm
@@ -7,6 +7,7 @@ use IO::Socket::UNIX; # core
 use Cwd qw(abs_path); # core
 use POSIX qw(:fcntl_h); # core
 use AnyEvent::Handle; # not core
+use AnyEvent::Util; # not core
 use Exporter 'import';
 use v5.10;
 
@@ -78,6 +79,10 @@ sub activate_i3 {
             POSIX::close(fileno($socket));
         }
 
+        # Make sure no file descriptors are open. Strangely, I got an open file
+        # descriptor pointing to AnyEvent/Impl/EV.pm when testing.
+        AnyEvent::Util::close_all_fds_except(0, 1, 2, 3);
+
         # Construct the command to launch i3. Use maximum debug level, disable
         # the interactive signalhandler to make it crash immediately instead.
         my $i3cmd = abs_path("../i3") . " -V -d all --disable-signalhandler";