diff --git a/nbqa/replace_source.py b/nbqa/replace_source.py
index 23d8c728..1414c922 100644
--- a/nbqa/replace_source.py
+++ b/nbqa/replace_source.py
@@ -157,7 +157,7 @@ def mutate(python_file: "Path", notebook: "Path", notebook_info: NotebookInfo) -
     notebook_info
         Information about notebook cells used for processing
     """
-    notebook_json = json.loads(notebook.read_text())
+    notebook_json = json.loads(notebook.read_text(encoding="utf-8"))
 
     pycells = _get_pycells(python_file)
     for code_cell_number, cell in enumerate(
@@ -167,7 +167,9 @@ def mutate(python_file: "Path", notebook: "Path", notebook_info: NotebookInfo) -
             continue
         cell["source"] = _get_new_source(code_cell_number, notebook_info, next(pycells))
 
-    notebook.write_text(f"{json.dumps(notebook_json, indent=1, ensure_ascii=False)}\n")
+    notebook.write_text(
+        f"{json.dumps(notebook_json, indent=1, ensure_ascii=False)}\n", encoding="utf-8"
+    )
 
 
 def _print_diff(code_cell_number: int, cell_diff: Iterator[str]) -> None:
@@ -211,7 +213,7 @@ def diff(python_file: "Path", notebook: "Path", notebook_info: NotebookInfo) ->
     notebook_info
         Information about notebook cells used for processing
     """
-    notebook_json = json.loads(notebook.read_text())
+    notebook_json = json.loads(notebook.read_text(encoding="utf-8"))
 
     pycells = _get_pycells(python_file)
 
diff --git a/nbqa/save_source.py b/nbqa/save_source.py
index a2cba9e0..e499e431 100644
--- a/nbqa/save_source.py
+++ b/nbqa/save_source.py
@@ -331,7 +331,7 @@ def main(
     NotebookInfo
 
     """
-    cells = json.loads(notebook.read_text())["cells"]
+    cells = json.loads(notebook.read_text(encoding="utf-8"))["cells"]
 
     result = []
     cell_mapping = {0: "cell_0:0"}
@@ -366,7 +366,9 @@ def main(
             result.append(re.sub(r";(\s*)$", "\\1", parsed_cell))
             line_number += len(parsed_cell.splitlines())
 
-    temp_python_file.write_text("".join(result).rstrip(NEWLINE) + NEWLINE)
+    temp_python_file.write_text(
+        "".join(result).rstrip(NEWLINE) + NEWLINE, encoding="utf-8"
+    )
 
     return NotebookInfo(
         cell_mapping, trailing_semicolons, temporary_lines, code_cells_to_ignore