diff --git a/platformio/builder/tools/piomisc.py b/platformio/builder/tools/piomisc.py
index 20768671..9c7bf548 100644
--- a/platformio/builder/tools/piomisc.py
+++ b/platformio/builder/tools/piomisc.py
@@ -80,12 +80,14 @@ class InoToCPPConverter(object):
         assert self._gcc_preprocess(contents, out_file)
         contents = fs.get_file_contents(out_file)
         contents = self._join_multiline_strings(contents)
-        fs.write_file_contents(out_file, self.append_prototypes(contents))
+        fs.write_file_contents(
+            out_file, self.append_prototypes(contents), errors="backslashreplace"
+        )
         return out_file
 
     def _gcc_preprocess(self, contents, out_file):
         tmp_path = mkstemp()[1]
-        fs.write_file_contents(tmp_path, contents)
+        fs.write_file_contents(tmp_path, contents, errors="backslashreplace")
         self.env.Execute(
             self.env.VerboseAction(
                 '$CXX -o "{0}" -x c++ -fpreprocessed -dD -E "{1}"'.format(
diff --git a/platformio/fs.py b/platformio/fs.py
index 017b653a..16dcb3e8 100644
--- a/platformio/fs.py
+++ b/platformio/fs.py
@@ -58,12 +58,19 @@ def get_file_contents(path):
             return fp.read()
 
 
-def write_file_contents(path, contents):
+def write_file_contents(path, contents, errors=None):
     try:
         with open(path, "w") as fp:
             return fp.write(contents)
     except UnicodeEncodeError:
-        with io.open(path, "w", encoding="latin-1", errors="backslashreplace") as fp:
+        if errors:
+            click.secho(
+                "Warning! There is a problem with contents encoding, please remove "
+                "invalid characters (non-ASCII or non-UT8) in %s" % path,
+                fg="yellow",
+                err=True,
+            )
+        with io.open(path, "w", encoding="latin-1", errors=errors) as fp:
             return fp.write(contents)