diff --git a/modules/js/src/make_umd.py b/modules/js/src/make_umd.py
index 08d9e39e13..bed6ee9bcc 100644
--- a/modules/js/src/make_umd.py
+++ b/modules/js/src/make_umd.py
@@ -69,13 +69,16 @@
 import os, sys, re, json, shutil
 from subprocess import Popen, PIPE, STDOUT
 
+PY3 = sys.version_info >= (3, 0)
+
 def make_umd(opencvjs, cvjs):
-    src = open(opencvjs, 'r+b')
-    dst = open(cvjs, 'w+b')
-    content = src.read()
-    dst.seek(0)
-    # inspired by https://github.com/umdjs/umd/blob/95563fd6b46f06bda0af143ff67292e7f6ede6b7/templates/returnExportsGlobal.js
-    dst.write(("""
+    with open(opencvjs, 'r+b') as src:
+        content = src.read()
+    if PY3:  # content is bytes
+        content = content.decode('utf-8')
+    with open(cvjs, 'w+b') as dst:
+        # inspired by https://github.com/umdjs/umd/blob/95563fd6b46f06bda0af143ff67292e7f6ede6b7/templates/returnExportsGlobal.js
+        dst.write(("""
 (function (root, factory) {
   if (typeof define === 'function' && define.amd) {
     // AMD. Register as an anonymous module.
@@ -103,7 +106,8 @@ def make_umd(opencvjs, cvjs):
     Module = {};
   return cv(Module);
 }));
-    """ % (content)).lstrip().encode())
+        """ % (content)).lstrip().encode('utf-8'))
+
 
 if __name__ == "__main__":
     if len(sys.argv) > 2:
diff --git a/platforms/js/build_js.py b/platforms/js/build_js.py
index 8012552215..0981c6656b 100644
--- a/platforms/js/build_js.py
+++ b/platforms/js/build_js.py
@@ -77,7 +77,9 @@ class Builder:
             rm_one(d)
 
     def get_cmake_cmd(self):
-        cmd = ["cmake",
+        cmd = [
+            "cmake",
+            "-DPYTHON_DEFAULT_EXECUTABLE=%s" % sys.executable,
                "-DENABLE_PIC=FALSE", # To workaround emscripten upstream backend issue https://github.com/emscripten-core/emscripten/issues/8761
                "-DCMAKE_BUILD_TYPE=Release",
                "-DCMAKE_TOOLCHAIN_FILE='%s'" % self.get_toolchain_file(),