diff --git a/third_party/flatbuffers/build_defs.bzl b/third_party/flatbuffers/build_defs.bzl
index 8f79cef90b5..e0fe1088992 100644
--- a/third_party/flatbuffers/build_defs.bzl
+++ b/third_party/flatbuffers/build_defs.bzl
@@ -379,13 +379,18 @@ def flatbuffer_py_strip_prefix_srcs(name, srcs = [], strip_prefix = ""):
         )
 
 def _concat_flatbuffer_py_srcs_impl(ctx):
-    # Merge all generated python files.
-    command = "find '%s' -name '*.py' -exec cat {} + | sed '/import flatbuffers/d'"
-    command += " | sed '1s/^/import flatbuffers\\'$'\\n/' > %s"
+    # Merge all generated python files. The files are concatenated and import
+    # statements are removed. Finally we import the flatbuffer runtime library.
+    # IMPORTANT: Our Windows shell does not support "find ... -exec" properly.
+    # If you're changing the commandline below, please build wheels and run smoke
+    # tests on all the three operating systems.
+    command = "echo 'import flatbuffers\n' > %s; "
+    command += "for f in $(find %s -name '*.py'); do cat $f | sed '/import flatbuffers/d' >> %s; done "
     ctx.actions.run_shell(
         inputs = ctx.attr.deps[0].files,
         outputs = [ctx.outputs.out],
         command = command % (
+            ctx.outputs.out.path,
             ctx.attr.deps[0].files.to_list()[0].path,
             ctx.outputs.out.path,
         ),