diff --git a/src/backend/bootstrap/bootstrap.c b/src/backend/bootstrap/bootstrap.c
index a5217773ffc..f3a7a007f77 100644
--- a/src/backend/bootstrap/bootstrap.c
+++ b/src/backend/bootstrap/bootstrap.c
@@ -334,6 +334,12 @@ BootstrapModeMain(int argc, char *argv[], bool check_only)
 
 	CreateSharedMemoryAndSemaphores();
 
+	/*
+	 * Estimate number of openable files.  This is essential too in --check
+	 * mode, because on some platforms semaphores count as open files.
+	 */
+	set_max_safe_fds();
+
 	/*
 	 * XXX: It might make sense to move this into its own function at some
 	 * point. Right now it seems like it'd cause more code duplication than
diff --git a/src/backend/tcop/postgres.c b/src/backend/tcop/postgres.c
index 3ce088f0bad..85902788181 100644
--- a/src/backend/tcop/postgres.c
+++ b/src/backend/tcop/postgres.c
@@ -4099,8 +4099,18 @@ PostgresSingleUserMain(int argc, char *argv[],
 	 */
 	InitializeWalConsistencyChecking();
 
+	/*
+	 * Create shared memory etc.  (Nothing's really "shared" in single-user
+	 * mode, but we must have these data structures anyway.)
+	 */
 	CreateSharedMemoryAndSemaphores();
 
+	/*
+	 * Estimate number of openable files.  This must happen after setting up
+	 * semaphores, because on some platforms semaphores count as open files.
+	 */
+	set_max_safe_fds();
+
 	/*
 	 * Remember stand-alone backend startup time,roughly at the same point
 	 * during startup that postmaster does so.