diff -up dovecot-2.2.36/src/auth/userdb-passwd.c.getpwentreset dovecot-2.2.36/src/auth/userdb-passwd.c
--- dovecot-2.2.36/src/auth/userdb-passwd.c.getpwentreset	2019-08-20 16:56:19.706885908 +0200
+++ dovecot-2.2.36/src/auth/userdb-passwd.c	2019-08-20 16:56:25.422867784 +0200
@@ -173,6 +173,9 @@ static void passwd_iterate_next(struct u
 			_ctx->callback(pw->pw_name, _ctx->context);
 			return;
 		}
+                /* getpwent might set errno to something even if it
+		   returns non-NULL. */
+		errno = 0;
 	}
 	if (errno != 0) {
 		i_error("getpwent() failed: %m");